# Reconstruct the array by replacing arr[i] with (arr[i-1]+1) % M

• Difficulty Level : Basic
• Last Updated : 25 Aug, 2021

Given an array of N elements and an integer M. Now, the array is modified by replacing some of the array elements with -1. The task is to print the original array.
The elements in the original array are related as, for every index i, a[i] = (a[i-1]+1)% M.
It is guaranteed that there is one non-zero value in the array.

Examples:

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```Input: arr[] = {5, -1, -1, 1, 2, 3}, M = 7
Output: 5 6 0 1 2 3
M = 7, so value at index 2 should be (5+1) % 7 = 6
value at index 3 should be (6+1) % 7 = 0

Input: arr[] = {5, -1, 7, -1, 9, 0}, M = 10
Output: 5 6 7 8 9 0 ```

Approach: First find the index of the non-negative value index i. Then simply go in two directions i.e. From i-1 to 0 and i+1 to n.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of above approach``#include ``using` `namespace` `std;` `void` `construct(``int` `n, ``int` `m, ``int` `a[])``{``    ``int` `ind = 0;` `    ``// Finding the index which is not -1``    ``for` `(``int` `i = 0; i < n; i++)``    ``{``        ``if` `(a[i] != -1)``        ``{``            ``ind = i;``            ``break``;``        ``}``    ``}``    ` `    ``// Calculating the values of``    ``// the indexes ind-1 to 0``    ``for` `(``int` `i = ind - 1; i > -1; i--)``    ``{``        ``if` `(a[i] == -1)``            ``a[i] = (a[i + 1] - 1 + m) % m;``    ``}``    ` `    ``// Calculating the values of``    ``// the indexes ind + 1 to n``    ``for` `(``int` `i = ind + 1; i < n; i++)``    ``{``        ``if` `(a[i] == -1)``            ``a[i] = (a[i - 1] + 1) % m;``    ``}``    ``for` `(``int` `i = 0; i < n; i++)``    ``{``        ``cout<< a[i] << ``" "``;``    ``}` `}` `// Driver code``int` `main()``{` `    ``int` `n = 6, m = 7;``    ``int` `a[] = { 5, -1, -1, 1, 2, 3 };``    ``construct(n, m, a);``    ``return` `0;``}` `// This code is contributed by 29AjayKumar`

## Java

 `// Java implementation of the above approach``class` `GFG``{``    ``static` `void` `construct(``int` `n, ``int` `m, ``int``[] a)``    ``{``        ``int` `ind = ``0``;` `        ``// Finding the index which is not -1``        ``for` `(``int` `i = ``0``; i < n; i++)``        ``{``            ``if` `(a[i] != -``1``)``            ``{``                ``ind = i;``                ``break``;``            ``}``        ``}``        ` `        ``// Calculating the values of``        ``// the indexes ind-1 to 0``        ``for` `(``int` `i = ind - ``1``; i > -``1``; i--)``        ``{``            ``if` `(a[i] == -``1``)``                ``a[i] = (a[i + ``1``] - ``1` `+ m) % m;``        ``}``        ` `        ``// Calculating the values of``        ``// the indexes ind + 1 to n``        ``for` `(``int` `i = ind + ``1``; i < n; i++)``        ``{``            ``if` `(a[i] == -``1``)``                ``a[i] = (a[i - ``1``] + ``1``) % m;``        ``}``        ``for` `(``int` `i = ``0``; i < n; i++)``        ``{``            ``System.out.print(a[i] + ``" "``);``        ``}` `    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `n = ``6``, m = ``7``;``        ``int``[] a = { ``5``, -``1``, -``1``, ``1``, ``2``, ``3` `};``        ``construct(n, m, a);``    ``}``}` `// This code is contributed by 29AjayKumar`

## Python3

 `# Python implementation of the above approach``def` `construct(n, m, a):``    ``ind ``=` `0` `    ``# Finding the index which is not -1``    ``for` `i ``in` `range``(n):``        ``if` `(a[i]!``=``-``1``):``            ``ind ``=` `i``            ``break` `    ``# Calculating the values of the indexes ind-1 to 0``    ``for` `i ``in` `range``(ind``-``1``, ``-``1``, ``-``1``):``        ``if` `(a[i]``=``=``-``1``):``            ``a[i]``=``(a[i ``+` `1``]``-``1` `+` `m)``%` `m` `    ``# Calculating the values of the indexes ind + 1 to n``    ``for` `i ``in` `range``(ind ``+` `1``, n):``        ``if``(a[i]``=``=``-``1``):``            ``a[i]``=``(a[i``-``1``]``+``1``)``%` `m``    ``print``(``*``a)` `# Driver code``n, m ``=` `6``, ``7``a ``=``[``5``, ``-``1``, ``-``1``, ``1``, ``2``, ``3``]``construct(n, m, a)`

## C#

 `// C# implementation of the above approach``using` `System;` `class` `GFG``{``    ``static` `void` `construct(``int` `n, ``int` `m, ``int``[] a)``    ``{``        ``int` `ind = 0;` `        ``// Finding the index which is not -1``        ``for` `(``int` `i = 0; i < n; i++)``        ``{``            ``if` `(a[i] != -1)``            ``{``                ``ind = i;``                ``break``;``            ``}``        ``}``        ` `        ``// Calculating the values of``        ``// the indexes ind-1 to 0``        ``for` `(``int` `i = ind - 1; i > -1; i--)``        ``{``            ``if` `(a[i] == -1)``                ``a[i] = (a[i + 1] - 1 + m) % m;``        ``}``        ` `        ``// Calculating the values of``        ``// the indexes ind + 1 to n``        ``for` `(``int` `i = ind + 1; i < n; i++)``        ``{``            ``if` `(a[i] == -1)``                ``a[i] = (a[i - 1] + 1) % m;``        ``}``        ``for` `(``int` `i = 0; i < n; i++)``        ``{``            ``Console.Write(a[i] + ``" "``);``        ``}` `    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``int` `n = 6, m = 7;``        ``int``[] a = { 5, -1, -1, 1, 2, 3 };``        ``construct(n, m, a);``    ``}``}` `// This code is contributed by 29AjayKumar`

## Javascript

 ``
Output:
`5 6 0 1 2 3`

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