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# Check if array elements are consecutive | Added Method 3

• Difficulty Level : Easy
• Last Updated : 23 Apr, 2021

Given an unsorted array of numbers, write a function that returns true if the array consists of consecutive numbers.
Examples:
a) If the array is {5, 2, 3, 1, 4}, then the function should return true because the array has consecutive numbers from 1 to 5.
b) If the array is {83, 78, 80, 81, 79, 82}, then the function should return true because the array has consecutive numbers from 78 to 83.
c) If the array is {34, 23, 52, 12, 3}, then the function should return false because the elements are not consecutive.
d) If the array is {7, 6, 5, 5, 3, 4}, then the function should return false because 5 and 5 are not consecutive.

Method 1 (Use Sorting)
1) Sort all the elements.
2) Do a linear scan of the sorted array. If the difference between the current element and the next element is anything other than 1, then return false. If all differences are 1, then return true.
Time Complexity: O(nLogn)
Method 2 (Use visited array)
The idea is to check for the following two conditions. If the following two conditions are true, then return true.
1) max – min + 1 = n where max is the maximum element in the array, min is the minimum element in the array and n is the number of elements in the array.
2) All elements are distinct.
To check if all elements are distinct, we can create a visited[] array of size n. We can map the ith element of input array arr[] to the visited array by using arr[i] – min as the index in visited[].

## C++

 `#include``#include` `/* Helper functions to get minimum and maximum in an array */``int` `getMin(``int` `arr[], ``int` `n);``int` `getMax(``int` `arr[], ``int` `n);` `/* The function checks if the array elements are consecutive``  ``If elements are consecutive, then returns true, else returns``  ``false */``bool` `areConsecutive(``int` `arr[], ``int` `n)``{``  ``if` `( n <  1 )``    ``return` `false``;` `  ``/* 1) Get the minimum element in array */``  ``int` `min = getMin(arr, n);` `  ``/* 2) Get the maximum element in array */``  ``int` `max = getMax(arr, n);` `  ``/* 3) max - min + 1 is equal to n,  then only check all elements */``  ``if` `(max - min  + 1 == n)``  ``{``      ``/* Create a temp array to hold visited flag of all elements.``         ``Note that, calloc is used here so that all values are initialized``         ``as false */``      ``bool` `*visited = (``bool` `*) ``calloc` `(n, ``sizeof``(``bool``));``      ``int` `i;``      ``for` `(i = 0; i < n; i++)``      ``{``         ``/* If we see an element again, then return false */``         ``if` `( visited[arr[i] - min] != ``false` `)``           ``return` `false``;` `         ``/* If visited first time, then mark the element as visited */``         ``visited[arr[i] - min] = ``true``;``      ``}` `      ``/* If all elements occur once, then return true */``      ``return` `true``;``  ``}` `  ``return` `false``; ``// if (max - min  + 1 != n)``}` `/* UTILITY FUNCTIONS */``int` `getMin(``int` `arr[], ``int` `n)``{``  ``int` `min = arr[0];``  ``for` `(``int` `i = 1; i < n; i++)``   ``if` `(arr[i] < min)``     ``min = arr[i];``  ``return` `min;``}` `int` `getMax(``int` `arr[], ``int` `n)``{``  ``int` `max = arr[0];``  ``for` `(``int` `i = 1; i < n; i++)``   ``if` `(arr[i] > max)``     ``max = arr[i];``  ``return` `max;``}` `/* Driver program to test above functions */``int` `main()``{``    ``int` `arr[]= {5, 4, 2, 3, 1, 6};``    ``int` `n = ``sizeof``(arr)/``sizeof``(arr[0]);``    ``if``(areConsecutive(arr, n) == ``true``)``        ``printf``(``" Array elements are consecutive "``);``    ``else``        ``printf``(``" Array elements are not consecutive "``);``    ``getchar``();``    ``return` `0;``}`

## Java

 `class` `AreConsecutive``{``    ``/* The function checks if the array elements are consecutive``       ``If elements are consecutive, then returns true, else returns``       ``false */``    ``boolean` `areConsecutive(``int` `arr[], ``int` `n)``    ``{``        ``if` `(n < ``1``)``            ``return` `false``;` `        ``/* 1) Get the minimum element in array */``        ``int` `min = getMin(arr, n);` `        ``/* 2) Get the maximum element in array */``        ``int` `max = getMax(arr, n);` `        ``/* 3) max - min + 1 is equal to n,  then only check all elements */``        ``if` `(max - min + ``1` `== n)``        ``{``            ``/* Create a temp array to hold visited flag of all elements.``               ``Note that, calloc is used here so that all values are initialized``               ``as false */``            ``boolean` `visited[] = ``new` `boolean``[n];``            ``int` `i;``            ``for` `(i = ``0``; i < n; i++)``            ``{``                ``/* If we see an element again, then return false */``                ``if` `(visited[arr[i] - min] != ``false``)``                    ``return` `false``;` `                ``/* If visited first time, then mark the element as visited */``                ``visited[arr[i] - min] = ``true``;``            ``}``            ` `            ``/* If all elements occur once, then return true */``            ``return` `true``;``        ``}``        ``return` `false``; ``// if (max - min  + 1 != n)``    ``}` `    ``/* UTILITY FUNCTIONS */``    ``int` `getMin(``int` `arr[], ``int` `n)``    ``{``        ``int` `min = arr[``0``];``        ``for` `(``int` `i = ``1``; i < n; i++)``        ``{``            ``if` `(arr[i] < min)``                ``min = arr[i];``        ``}``        ``return` `min;``    ``}` `    ``int` `getMax(``int` `arr[], ``int` `n)``    ``{``        ``int` `max = arr[``0``];``        ``for` `(``int` `i = ``1``; i < n; i++)``        ``{``            ``if` `(arr[i] > max)``                ``max = arr[i];``        ``}``        ``return` `max;``    ``}` `    ``/* Driver program to test above functions */``    ``public` `static` `void` `main(String[] args)``    ``{``        ``AreConsecutive consecutive = ``new` `AreConsecutive();``        ``int` `arr[] = {``5``, ``4``, ``2``, ``3``, ``1``, ``6``};``        ``int` `n = arr.length;``        ``if` `(consecutive.areConsecutive(arr, n) == ``true``)``            ``System.out.println(``"Array elements are consecutive"``);``        ``else``            ``System.out.println(``"Array elements are not consecutive"``);``    ``}``}` `// This code has been contributed by Mayank Jaiswal`

## Python3

 `# Helper functions to get Minimum and``# Maximum in an array` `# The function checks if the array elements``# are consecutive. If elements are consecutive,``# then returns true, else returns false``def` `areConsecutive(arr, n):` `    ``if` `( n < ``1` `):``        ``return` `False``    ` `    ``# 1) Get the Minimum element in array */``    ``Min` `=` `min``(arr)``    ` `    ``# 2) Get the Maximum element in array */``    ``Max` `=` `max``(arr)``    ` `    ``# 3) Max - Min + 1 is equal to n,``    ``# then only check all elements */``    ``if` `(``Max` `-` `Min` `+` `1` `=``=` `n):``        ` `        ``# Create a temp array to hold visited``        ``# flag of all elements. Note that, calloc``        ``# is used here so that all values are``        ``# initialized as false``        ``visited ``=` `[``False` `for` `i ``in` `range``(n)]``    ` `        ``for` `i ``in` `range``(n):``            ` `            ``# If we see an element again,``            ``# then return false */``            ``if` `(visited[arr[i] ``-` `Min``] !``=` `False``):``                ``return` `False``    ` `            ``# If visited first time, then mark``            ``# the element as visited */``            ``visited[arr[i] ``-` `Min``] ``=` `True``    ` `        ``# If all elements occur once,``        ``# then return true */``        ``return` `True``    ` `    ``return` `False` `# if (Max - Min + 1 != n)` `# Driver Code``arr ``=` `[``5``, ``4``, ``2``, ``3``, ``1``, ``6``]``n ``=` `len``(arr)``if``(areConsecutive(arr, n) ``=``=` `True``):``    ``print``(``"Array elements are consecutive "``)``else``:``    ``print``(``"Array elements are not consecutive "``)` `# This code is contributed by mohit kumar`

## C#

 `using` `System;` `class` `GFG {``    ` `    ``/* The function checks if the array elements``    ``are consecutive If elements are consecutive,``    ``then returns true, else returns    false */``    ``static` `bool` `areConsecutive(``int` `[]arr, ``int` `n)``    ``{``        ``if` `(n < 1)``            ``return` `false``;` `        ``/* 1) Get the minimum element in array */``        ``int` `min = getMin(arr, n);` `        ``/* 2) Get the maximum element in array */``        ``int` `max = getMax(arr, n);` `        ``/* 3) max - min + 1 is equal to n, then``        ``only check all elements */``        ``if` `(max - min + 1 == n)``        ``{``            ` `            ``/* Create a temp array to hold visited``            ``flag of all elements. Note that, calloc``            ``is used here so that all values are``            ``initialized as false */``            ``bool` `[]visited = ``new` `bool``[n];``            ``int` `i;``            ` `            ``for` `(i = 0; i < n; i++)``            ``{``                ` `                ``/* If we see an element again, then``                ``return false */``                ``if` `(visited[arr[i] - min] != ``false``)``                    ``return` `false``;` `                ``/* If visited first time, then mark``                ``the element as visited */``                ``visited[arr[i] - min] = ``true``;``            ``}``            ` `            ``/* If all elements occur once, then``            ``return true */``            ``return` `true``;``        ``}``        ``return` `false``; ``// if (max - min + 1 != n)``    ``}` `    ``/* UTILITY FUNCTIONS */``    ``static` `int` `getMin(``int` `[]arr, ``int` `n)``    ``{``        ``int` `min = arr[0];``        ` `        ``for` `(``int` `i = 1; i < n; i++)``        ``{``            ``if` `(arr[i] < min)``                ``min = arr[i];``        ``}``        ` `        ``return` `min;``    ``}` `    ``static` `int` `getMax(``int` `[]arr, ``int` `n)``    ``{``        ``int` `max = arr[0];``        ` `        ``for` `(``int` `i = 1; i < n; i++)``        ``{``            ``if` `(arr[i] > max)``                ``max = arr[i];``        ``}``        ` `        ``return` `max;``    ``}` `    ``/* Driver program to test above functions */``    ``public` `static` `void` `Main()``    ``{``        ``int` `[]arr = {5, 4, 2, 3, 1, 6};``        ``int` `n = arr.Length;``        ` `        ``if` `(areConsecutive(arr, n) == ``true``)``            ``Console.Write(``"Array elements are"``                              ``+ ``" consecutive"``);``        ``else``            ``Console.Write(``"Array elements are"``                         ``+ ``" not consecutive"``);``    ``}``}` `// This code is contributed by nitin mittal.`

## PHP

 ` ``\$max``)``            ``\$max` `= ``\$arr``[``\$i``];``    ``return` `\$max``;``}` `// Driver Code``\$arr` `= ``array``(5, 4, 2, 3, 1, 6);``\$n` `= ``count``(``\$arr``);``if``(areConsecutive(``\$arr``, ``\$n``) == true)``    ``echo` `"Array elements are consecutive "``;``else``    ``echo` `"Array elements are not consecutive "``;``    ` `// This code is contributed by rathbhupendra``?>`

## Javascript

 ``

Time Complexity: O(n)
Extra Space: O(n)

Output:

`Array elements are consecutive`

Method 3 (Mark visited array elements as negative)
This method is O(n) time complexity and O(1) extra space, but it changes the original array, and it works only if all numbers are positive. We can get the original array by adding an extra step though. It is an extension of method 2, and it has the same two steps.
1) max – min + 1 = n where max is the maximum element in the array, min is the minimum element in the array and n is the number of elements in the array.
2) All elements are distinct.
In this method, the implementation of step 2 differs from method 2. Instead of creating a new array, we modify the input array arr[] to keep track of visited elements. The idea is to traverse the array and for each index i (where 0 ≤ i < n), make arr[arr[i] – min]] as a negative value. If we see a negative value again then there is repetition.

## C++

 `#include``#include` `/* Helper functions to get minimum and maximum in an array */``int` `getMin(``int` `arr[], ``int` `n);``int` `getMax(``int` `arr[], ``int` `n);` `/* The function checks if the array elements are consecutive``  ``If elements are consecutive, then returns true, else returns``  ``false */``bool` `areConsecutive(``int` `arr[], ``int` `n)``{` `    ``if` `( n <  1 )``        ``return` `false``;` `    ``/* 1) Get the minimum element in array */``    ``int` `min = getMin(arr, n);` `    ``/* 2) Get the maximum element in array */``    ``int` `max = getMax(arr, n);` `    ``/* 3) max - min + 1 is equal to n then only check all elements */``    ``if` `(max - min  + 1 == n)``    ``{``        ``int` `i;``        ``for``(i = 0; i < n; i++)``        ``{``            ``int` `j;` `            ``if` `(arr[i] < 0)``                ``j = -arr[i] - min;``            ``else``                ``j = arr[i] - min;` `            ``// if the value at index j is negative then``            ``// there is repetition``            ``if` `(arr[j] > 0)``                ``arr[j] = -arr[j];``            ``else``                ``return` `false``;``        ``}` `        ``/* If we do not see a negative value then all elements``           ``are distinct */``        ``return` `true``;``    ``}` `    ``return` `false``; ``// if (max - min  + 1 != n)``}` `/* UTILITY FUNCTIONS */``int` `getMin(``int` `arr[], ``int` `n)``{``    ``int` `min = arr[0];``    ``for` `(``int` `i = 1; i < n; i++)``        ``if` `(arr[i] < min)``            ``min = arr[i];``    ``return` `min;``}` `int` `getMax(``int` `arr[], ``int` `n)``{``    ``int` `max = arr[0];``    ``for` `(``int` `i = 1; i < n; i++)``        ``if` `(arr[i] > max)``            ``max = arr[i];``    ``return` `max;``}` `/* Driver program to test above functions */``int` `main()``{``    ``int` `arr[]= {1, 4, 5, 3, 2, 6};``    ``int` `n = ``sizeof``(arr)/``sizeof``(arr[0]);``    ``if``(areConsecutive(arr, n) == ``true``)``        ``printf``(``" Array elements are consecutive "``);``    ``else``        ``printf``(``" Array elements are not consecutive "``);``    ``getchar``();``    ``return` `0;``}`

## Java

 `class` `AreConsecutive``{``    ``/* The function checks if the array elements are consecutive``       ``If elements are consecutive, then returns true, else returns``       ``false */``    ``boolean` `areConsecutive(``int` `arr[], ``int` `n)``    ``{``        ``if` `(n < ``1``)``            ``return` `false``;` `        ``/* 1) Get the minimum element in array */``        ``int` `min = getMin(arr, n);` `        ``/* 2) Get the maximum element in array */``        ``int` `max = getMax(arr, n);` `        ``/* 3) max-min+1 is equal to n then only check all elements */``        ``if` `(max - min + ``1` `== n)``        ``{``            ``int` `i;``            ``for` `(i = ``0``; i < n; i++)``            ``{``                ``int` `j;` `                ``if` `(arr[i] < ``0``)``                    ``j = -arr[i] - min;``                ``else``                    ``j = arr[i] - min;` `                ``// if the value at index j is negative then``                ``// there is repitition``                ``if` `(arr[j] > ``0``)``                    ``arr[j] = -arr[j];``                ``else``                    ``return` `false``;``            ``}` `            ``/* If we do not see a negative value then all elements``               ``are distinct */``            ``return` `true``;``        ``}` `        ``return` `false``; ``// if (max-min+1 != n)``    ``}` `    ``/* UTILITY FUNCTIONS */``    ``int` `getMin(``int` `arr[], ``int` `n)``    ``{``        ``int` `min = arr[``0``];``        ``for` `(``int` `i = ``1``; i < n; i++)``        ``{``            ``if` `(arr[i] < min)``                ``min = arr[i];``        ``}``        ``return` `min;``    ``}` `    ``int` `getMax(``int` `arr[], ``int` `n)``    ``{``        ``int` `max = arr[``0``];``        ``for` `(``int` `i = ``1``; i < n; i++)``        ``{``            ``if` `(arr[i] > max)``                ``max = arr[i];``        ``}``        ``return` `max;``    ``}` `    ``/* Driver program to test above functions */``    ``public` `static` `void` `main(String[] args)``    ``{``        ``AreConsecutive consecutive = ``new` `AreConsecutive();``        ``int` `arr[] = {``5``, ``4``, ``2``, ``3``, ``1``, ``6``};``        ``int` `n = arr.length;``        ``if` `(consecutive.areConsecutive(arr, n) == ``true``)``            ``System.out.println(``"Array elements are consecutive"``);``        ``else``            ``System.out.println(``"Array elements are not consecutive"``);``    ``}``}` `// This code is contributed by Mayank Jaiswal`

## Python 3

 `# Helper functions to get minimum and``# maximum in an array` `# The function checks if the array``# elements are consecutive. If elements``# are consecutive, then returns true,``# else returns false``def` `areConsecutive(arr, n):` `    ``if` `( n < ``1` `):``        ``return` `False` `    ``# 1) Get the minimum element in array``    ``min` `=` `getMin(arr, n)` `    ``# 2) Get the maximum element in array``    ``max` `=` `getMax(arr, n)` `    ``# 3) max - min + 1 is equal to n``    ``# then only check all elements``    ``if` `(``max` `-` `min` `+` `1` `=``=` `n):` `        ``for` `i ``in` `range``(n):` `            ``if` `(arr[i] < ``0``):``                ``j ``=` `-``arr[i] ``-` `min``            ``else``:``                ``j ``=` `arr[i] ``-` `min` `            ``# if the value at index j is negative``            ``# then there is repetition``            ``if` `(arr[j] > ``0``):``                ``arr[j] ``=` `-``arr[j]``            ``else``:``                ``return` `False` `        ``# If we do not see a negative value``        ``# then all elements are distinct``        ``return` `True` `    ``return` `False`     `# if (max - min + 1 != n)` `# UTILITY FUNCTIONS``def` `getMin(arr, n):``    ` `    ``min` `=` `arr[``0``]``    ``for` `i ``in` `range``(``1``, n):``        ``if` `(arr[i] < ``min``):``            ``min` `=` `arr[i]``    ``return` `min` `def` `getMax(arr, n):``    ``max` `=` `arr[``0``]``    ``for` `i ``in` `range``(``1``, n):``        ``if` `(arr[i] > ``max``):``            ``max` `=` `arr[i]``    ``return` `max` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ` `    ``arr ``=` `[``1``, ``4``, ``5``, ``3``, ``2``, ``6``]``    ``n ``=` `len``(arr)``    ``if``(areConsecutive(arr, n) ``=``=` `True``):``        ``print``(``" Array elements are consecutive "``)``    ``else``:``        ``print``(``" Array elements are not consecutive "``)` `# This code is contributed by ita_c`

## C#

 `using` `System;` `class` `GFG {``    ` `    ``/* The function checks if the array``    ``elements are consecutive If elements``    ``are consecutive, then returns true,``    ``else returns false */``    ``static` `bool` `areConsecutive(``int` `[]arr, ``int` `n)``    ``{``        ``if` `(n < 1)``            ``return` `false``;` `        ``/* 1) Get the minimum element in``        ``array */``        ``int` `min = getMin(arr, n);` `        ``/* 2) Get the maximum element in``        ``array */``        ``int` `max = getMax(arr, n);` `        ``/* 3) max-min+1 is equal to n then``        ``only check all elements */``        ``if` `(max - min + 1 == n)``        ``{``            ``int` `i;``            ``for` `(i = 0; i < n; i++)``            ``{``                ``int` `j;` `                ``if` `(arr[i] < 0)``                    ``j = -arr[i] - min;``                ``else``                    ``j = arr[i] - min;` `                ``// if the value at index j``                ``// is negative then``                ``// there is repitition``                ``if` `(arr[j] > 0)``                    ``arr[j] = -arr[j];``                ``else``                    ``return` `false``;``            ``}` `            ``/* If we do not see a negative``            ``value then all elements``            ``are distinct */``            ``return` `true``;``        ``}` `        ``// if (max-min+1 != n)``        ``return` `false``;``    ``}` `    ``/* UTILITY FUNCTIONS */``    ``static` `int` `getMin(``int` `[]arr, ``int` `n)``    ``{``        ``int` `min = arr[0];``        ``for` `(``int` `i = 1; i < n; i++)``        ``{``            ``if` `(arr[i] < min)``                ``min = arr[i];``        ``}``        ``return` `min;``    ``}` `    ``static` `int` `getMax(``int` `[]arr, ``int` `n)``    ``{``        ``int` `max = arr[0];``        ``for` `(``int` `i = 1; i < n; i++)``        ``{``            ``if` `(arr[i] > max)``                ``max = arr[i];``        ``}``        ``return` `max;``    ``}` `    ``/* Driver program to test above``    ``functions */``    ``public` `static` `void` `Main()``    ``{``        ``int` `[]arr = {5, 4, 2, 3, 1, 6};``        ``int` `n = arr.Length;``        ` `        ``if` `(areConsecutive(arr, n) == ``true``)``            ``Console.Write(``"Array elements "``                      ``+ ``"are consecutive"``);``        ``else``            ``Console.Write(``"Array elements "``                  ``+ ``"are not consecutive"``);``    ``}``}` `// This code is contributed by nitin mittal.`

## PHP

 ` 0)``                ``\$arr``[``\$j``] = -``\$arr``[``\$j``];``            ``else``                ``return` `false;``        ``}` `        ``/* If we do not see a negative value``        ``then all elements are distinct */``        ``return` `true;``    ``}` `    ``return` `false; ``// if (max - min + 1 != n)``}` `/* UTILITY FUNCTIONS */``function` `getMin( ``\$arr``, ``\$n``)``{``    ``\$min` `= ``\$arr``[0];``    ``for` `( ``\$i` `= 1; ``\$i` `< ``\$n``; ``\$i``++)``        ``if` `(``\$arr``[``\$i``] < ``\$min``)``            ``\$min` `= ``\$arr``[``\$i``];``    ``return` `\$min``;``}` `function` `getMax( ``\$arr``, ``\$n``)``{``    ``\$max` `= ``\$arr``[0];``    ``for` `( ``\$i` `= 1; ``\$i` `< ``\$n``; ``\$i``++)``        ``if` `(``\$arr``[``\$i``] > ``\$max``)``            ``\$max` `= ``\$arr``[``\$i``];``    ``return` `\$max``;``}` `/* Driver program to test above functions */``    ``\$arr``= ``array``(1, 4, 5, 3, 2, 6);``    ``\$n` `= ``count``(``\$arr``);``    ``if``(areConsecutive(``\$arr``, ``\$n``) == true)``        ``echo` `" Array elements are consecutive "``;``    ``else``        ``echo` `" Array elements are not consecutive "``;`  `// This code is contributed by anuj_67.``?>`

## Javascript

 ``

Note that this method might not work for negative numbers. For example, it returns false for {2, 1, 0, -3, -1, -2}.
Time Complexity: O(n)
Extra Space: O(1)

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