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# Find start and ending index of an element in an unsorted array

Given an array of integers, task is to find the starting and ending position of a given key.

Examples:

```Input : arr[] = {1, 2, 3, 4, 5, 5}
Key = 5
Output :  Start index: 4
Last index: 5
Explanation: Starting index where 5
is present is 4 and ending index is 5.

Input :arr[] = {1, 3, 7, 8, 6},
Key = 2
Output : Key not present in array

Input :arr[] = {1, 8, 7, 8, 6},
Key = 7
Output : Only one occurrence of
key is present at index 2```
Recommended Practice

We traverse array from beginning to find first occurrence. If element is present, then we traverse from end also to find last occurrence.

Implementation:

## C++

 `// CPP program to find starting and ending``// indexes of repeated numbers in an array``#include ``using` `namespace` `std;`` ` `// Function to find starting and end index``void` `findIndex(``int` `a[], ``int` `n, ``int` `key)``{``    ``int` `start = -1;`` ` `    ``// Traverse from beginning to find``    ``// first occurrence``    ``for` `(``int` `i = 0; i < n; i++) {``        ``if` `(a[i] == key) {``            ``start = i;``            ``break``;``        ``}``    ``}`` ` `    ``if` `(start == -1) {``        ``cout << ``"Key not present in array"``;``        ``return``;``    ``}`` ` `    ``// Traverse from end to find last``    ``// occurrence.``    ``int` `end = start;``    ``for` `(``int` `i = n - 1; i >= start; i--) {``        ``if` `(a[i] == key) {``            ``end = i;``            ``break``;``        ``}``    ``}``    ``if` `(start == end)``        ``cout << ``"Only one key is present at index : "``             ``<< start;``    ``else` `{``        ``cout << ``"Start index: "` `<< start;``        ``cout << ``"\n"``;``        ``cout << ``"Last index: "` `<< end;``    ``}``}`` ` `// Driver Code``int` `main()``{``    ``int` `a[] = { 1, 2, 7, 8, 8, 9, 8, 0, 0, 0, 8 };``    ``int` `n = ``sizeof``(a) / ``sizeof``(a);`` ` `    ``// Key to find``    ``int` `key = 8;`` ` `    ``// Calling function``    ``findIndex(a, n, key);`` ` `    ``return` `0;``}`

## Java

 `// Java program to find starting and ending``// indexes of repeated numbers in an array`` ` `class` `Test {``    ``// Function to find starting and end index``    ``static` `void` `findIndex(``int` `a[], ``int` `n, ``int` `key)``    ``{``        ``int` `start = -``1``;`` ` `        ``// Traverse from beginning to find``        ``// first occurrence``        ``for` `(``int` `i = ``0``; i < n; i++) {``            ``if` `(a[i] == key) {``                ``start = i;``                ``break``;``            ``}``        ``}`` ` `        ``if` `(start == -``1``) {``            ``System.out.println(``"Key not present in array"``);``            ``return``;``        ``}`` ` `        ``// Traverse from end to find last``        ``// occurrence.``        ``int` `end = start;``        ``for` `(``int` `i = n - ``1``; i >= start; i--) {``            ``if` `(a[i] == key) {``                ``end = i;``                ``break``;``            ``}``        ``}``        ``if` `(start == end)``            ``System.out.println(``"Only one key is present at index : "` `+ start);``        ``else` `{``            ``System.out.println(``"Start index: "` `+ start);``            ``System.out.println(``"Last index: "` `+ end);``        ``}``    ``}`` ` `    ``// Driver method``    ``public` `static` `void` `main(String args[])``    ``{``        ``int` `a[] = { ``1``, ``2``, ``7``, ``8``, ``8``, ``9``, ``8``, ``0``, ``0``, ``0``, ``8` `};`` ` `        ``// Key to find``        ``int` `key = ``8``;`` ` `        ``// Calling method``        ``findIndex(a, a.length, key);``    ``}``}`

## Python3

 `# Python3 code to find starting and ending``# indexes of repeated numbers in an array`` ` `# Function to find starting and end index``def` `findIndex (a, n, key ):``    ``start ``=` `-``1``     ` `    ``# Traverse from beginning to find``    ``# first occurrence``    ``for` `i ``in` `range``(n):``        ``if` `a[i] ``=``=` `key:``            ``start ``=` `i``            ``break`` ` `    ``if` `start ``=``=` `-``1``:``        ``print``(``"Key not present in array"``)``        ``return` `0``     ` `    ``# Traverse from end to find last``    ``# occurrence.``    ``end ``=` `start``    ``for` `i ``in` `range``(n``-``1``, start ``-` `1``, ``-``1``):``        ``if` `a[i] ``=``=` `key:``            ``end ``=` `i``            ``break``    ``if` `start ``=``=` `end:``        ``print``(``"Only one key is present at index : "``, start)``    ``else``:``        ``print``(``"Start index: "``, start)``        ``print``(``"Last index: "``, end)`` ` `# Driver Code``a ``=` `[``1``, ``2``, ``7``, ``8``, ``8``, ``9``, ``8``, ``0``, ``0``, ``0``, ``8``]``n ``=` `len``(a)`` ` `# Key to find``key ``=` `8`` ` `# Calling function``findIndex(a, n, key)`` ` `# This code is contributed by "Sharad_Bhardwaj".`

## C#

 `// C# program to find starting and ending``// indexes of repeated numbers in an array``using` `System;`` ` `class` `GFG {`` ` `    ``// Function to find starting and``    ``// end index``    ``static` `void` `findIndex(``int``[] a, ``int` `n,``                          ``int` `key)``    ``{``        ``int` `start = -1;`` ` `        ``// Traverse from beginning to``        ``// find first occurrence``        ``for` `(``int` `i = 0; i < n; i++) {``            ``if` `(a[i] == key) {``                ``start = i;``                ``break``;``            ``}``        ``}`` ` `        ``if` `(start == -1) {``            ``Console.WriteLine(``"Key not "``                              ``+ ``"present in array"``);``            ``return``;``        ``}`` ` `        ``// Traverse from end to find last``        ``// occurrence.``        ``int` `end = start;``        ``for` `(``int` `i = n - 1; i >= start; i--) {``            ``if` `(a[i] == key) {``                ``end = i;``                ``break``;``            ``}``        ``}``        ``if` `(start == end)``            ``Console.WriteLine(``"Only one key is"``                              ``+ ``" present at index : "``                              ``+ start);``        ``else` `{``            ``Console.WriteLine(``"Start index: "``                              ``+ start);`` ` `            ``Console.WriteLine(``"Last index: "``                              ``+ end);``        ``}``    ``}`` ` `    ``// Driver method``    ``public` `static` `void` `Main()``    ``{``        ``int``[] a = { 1, 2, 7, 8, 8, 9,``                    ``8, 0, 0, 0, 8 };`` ` `        ``// Key to find``        ``int` `key = 8;`` ` `        ``// Calling method``        ``findIndex(a, a.Length, key);``    ``}``}`` ` `// This code is contributed by parashar.`

## PHP

 ` ``\$value``) {``         ` `        ``// If current element is equal ``        ``// to the given key``        ``if``(``\$find` `=== ``\$value``){``             ` `            ``// If starting index hasn't been set``            ``if``(``\$start``==-1)``                ``\$start` `= ``\$key``;``            ``\$end` `= ``\$key``;``        ``}``    ``}`` ` `    ``// If key is not present in the array``    ``if``(``\$start``==-1){``        ``return` `"Key not present in array"``;``    ``}``    ``if``(``\$end` `== ``\$start``){``        ``return` `"Only one key is present "``.``" at index : "``. ``\$start``;``    ``}``    ``return` `"Start index: "``.``\$start``. ``"\nLast index: "``.``\$end``;``}`` ` `// Driver code``\$a` `= ``array``(1, 2, 7, 8, 8, 9, 8, 0, 0, 0, 8); `` ` `// Key to find ``\$key` `= 8; `` ` `// Calling function ``echo` `findIndex(``\$a``, ``\$key``);``?>`

## Javascript

 ``

Output

```Start index: 3
Last index: 10```

Time Complexity: Worst case time complexity is O(N), ( when we traverse the whole array and don’t find the element’s start and last indices), where N represents the size of the given array. and best case time complexity will be O(1), when start index is ‘0’ and last index is ‘n – 1’.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Related Article:
Find first and last occurrences of an element in a sorted array

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