Given an array of random numbers, Push all the zero’s of a given array to the end of the array. For example, if the given arrays is {1, 9, 8, 4, 0, 0, 2, 7, 0, 6, 0}, it should be changed to {1, 9, 8, 4, 2, 7, 6, 0, 0, 0, 0}. The order of all other elements should be same. Expected time complexity is O(n) and extra space is O(1).**Example:**

Input : arr[] = {1, 2, 0, 4, 3, 0, 5, 0}; Output : arr[] = {1, 2, 4, 3, 5, 0, 0}; Input : arr[] = {1, 2, 0, 0, 0, 3, 6}; Output : arr[] = {1, 2, 3, 6, 0, 0, 0};

There can be many ways to solve this problem. Following is a simple and interesting way to solve this problem.

Traverse the given array ‘arr’ from left to right. While traversing, maintain count of non-zero elements in array. Let the count be ‘count’. For every non-zero element arr[i], put the element at ‘arr[count]’ and increment ‘count’. After complete traversal, all non-zero elements have already been shifted to front end and ‘count’ is set as index of first 0. Now all we need to do is that run a loop which makes all elements zero from ‘count’ till end of the array.

Below is the implementation of the above approach.

## C++

`// A C++ program to move all zeroes at the end of array` `#include <iostream>` `using` `namespace` `std;` `// Function which pushes all zeros to end of an array.` `void` `pushZerosToEnd(` `int` `arr[], ` `int` `n)` `{` ` ` `int` `count = 0; ` `// Count of non-zero elements` ` ` `// Traverse the array. If element encountered is non-` ` ` `// zero, then replace the element at index 'count'` ` ` `// with this element` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `if` `(arr[i] != 0)` ` ` `arr[count++] = arr[i]; ` `// here count is` ` ` `// incremented` ` ` `// Now all non-zero elements have been shifted to` ` ` `// front and 'count' is set as index of first 0.` ` ` `// Make all elements 0 from count to end.` ` ` `while` `(count < n)` ` ` `arr[count++] = 0;` `}` `// Driver program to test above function` `int` `main()` `{` ` ` `int` `arr[] = {1, 9, 8, 4, 0, 0, 2, 7, 0, 6, 0, 9};` ` ` `int` `n = ` `sizeof` `(arr) / ` `sizeof` `(arr[0]);` ` ` `pushZerosToEnd(arr, n);` ` ` `cout << ` `"Array after pushing all zeros to end of array :\n"` `;` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `cout << arr[i] << ` `" "` `;` ` ` `return` `0;` `}` |

## Java

`/* Java program to push zeroes to back of array */` `import` `java.io.*;` `class` `PushZero` `{` ` ` `// Function which pushes all zeros to end of an array.` ` ` `static` `void` `pushZerosToEnd(` `int` `arr[], ` `int` `n)` ` ` `{` ` ` `int` `count = ` `0` `; ` `// Count of non-zero elements` ` ` `// Traverse the array. If element encountered is` ` ` `// non-zero, then replace the element at index 'count'` ` ` `// with this element` ` ` `for` `(` `int` `i = ` `0` `; i < n; i++)` ` ` `if` `(arr[i] != ` `0` `)` ` ` `arr[count++] = arr[i]; ` `// here count is` ` ` `// incremented` ` ` `// Now all non-zero elements have been shifted to` ` ` `// front and 'count' is set as index of first 0.` ` ` `// Make all elements 0 from count to end.` ` ` `while` `(count < n)` ` ` `arr[count++] = ` `0` `;` ` ` `}` ` ` `/*Driver function to check for above functions*/` ` ` `public` `static` `void` `main (String[] args)` ` ` `{` ` ` `int` `arr[] = {` `1` `, ` `9` `, ` `8` `, ` `4` `, ` `0` `, ` `0` `, ` `2` `, ` `7` `, ` `0` `, ` `6` `, ` `0` `, ` `9` `};` ` ` `int` `n = arr.length;` ` ` `pushZerosToEnd(arr, n);` ` ` `System.out.println(` `"Array after pushing zeros to the back: "` `);` ` ` `for` `(` `int` `i=` `0` `; i<n; i++)` ` ` `System.out.print(arr[i]+` `" "` `);` ` ` `}` `}` `/* This code is contributed by Devesh Agrawal */` |

## Python3

`# Python3 code to move all zeroes` `# at the end of array` `# Function which pushes all` `# zeros to end of an array.` `def` `pushZerosToEnd(arr, n):` ` ` `count ` `=` `0` `# Count of non-zero elements` ` ` ` ` `# Traverse the array. If element` ` ` `# encountered is non-zero, then` ` ` `# replace the element at index` ` ` `# 'count' with this element` ` ` `for` `i ` `in` `range` `(n):` ` ` `if` `arr[i] !` `=` `0` `:` ` ` ` ` `# here count is incremented` ` ` `arr[count] ` `=` `arr[i]` ` ` `count` `+` `=` `1` ` ` ` ` `# Now all non-zero elements have been` ` ` `# shifted to front and 'count' is set` ` ` `# as index of first 0. Make all` ` ` `# elements 0 from count to end.` ` ` `while` `count < n:` ` ` `arr[count] ` `=` `0` ` ` `count ` `+` `=` `1` ` ` `# Driver code` `arr ` `=` `[` `1` `, ` `9` `, ` `8` `, ` `4` `, ` `0` `, ` `0` `, ` `2` `, ` `7` `, ` `0` `, ` `6` `, ` `0` `, ` `9` `]` `n ` `=` `len` `(arr)` `pushZerosToEnd(arr, n)` `print` `(` `"Array after pushing all zeros to end of array:"` `)` `print` `(arr)` `# This code is contributed by "Abhishek Sharma 44"` |

## C#

`/* C# program to push zeroes to back of array */` `using` `System;` `class` `PushZero` `{` ` ` `// Function which pushes all zeros` ` ` `// to end of an array.` ` ` `static` `void` `pushZerosToEnd(` `int` `[]arr, ` `int` `n)` ` ` `{` ` ` `// Count of non-zero elements` ` ` `int` `count = 0;` ` ` ` ` `// Traverse the array. If element encountered is` ` ` `// non-zero, then replace the element` ` ` `// at index â..countâ.. with this element` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `if` `(arr[i] != 0)` ` ` ` ` `// here count is incremented` ` ` `arr[count++] = arr[i];` ` ` ` ` `// Now all non-zero elements have been shifted to` ` ` `// front and â..countâ.. is set as index of first 0.` ` ` `// Make all elements 0 from count to end.` ` ` `while` `(count < n)` ` ` `arr[count++] = 0;` ` ` `}` ` ` ` ` `// Driver function` ` ` `public` `static` `void` `Main ()` ` ` `{` ` ` `int` `[]arr = {1, 9, 8, 4, 0, 0, 2, 7, 0, 6, 0, 9};` ` ` `int` `n = arr.Length;` ` ` `pushZerosToEnd(arr, n);` ` ` `Console.WriteLine(` `"Array after pushing all zeros to the back: "` `);` ` ` `for` `(` `int` `i = 0; i < n; i++)` ` ` `Console.Write(arr[i] +` `" "` `);` ` ` `}` `}` `/* This code is contributed by Anant Agrawal */` |

## PHP

`<?php` `// A PHP program to move all` `// zeroes at the end of array` `// Function which pushes all` `// zeros to end of an array.` `function` `pushZerosToEnd(&` `$arr` `, ` `$n` `)` `{` ` ` `// Count of non-zero elements` ` ` `$count` `= 0;` ` ` `// Traverse the array. If` ` ` `// element encountered is` ` ` `// non-zero, then replace` ` ` `// the element at index` ` ` `// 'count' with this element` ` ` `for` `(` `$i` `= 0; ` `$i` `< ` `$n` `; ` `$i` `++)` ` ` `if` `(` `$arr` `[` `$i` `] != 0)` ` ` `// here count is incremented` ` ` `$arr` `[` `$count` `++] = ` `$arr` `[` `$i` `];` ` ` `// Now all non-zero elements` ` ` `// have been shifted to front` ` ` `// and 'count' is set as index ` ` ` `// of first 0. Make all elements` ` ` `// 0 from count to end.` ` ` `while` `(` `$count` `< ` `$n` `)` ` ` `$arr` `[` `$count` `++] = 0;` `}` `// Driver Code` `$arr` `= ` `array` `(1, 9, 8, 4, 0, 0,` ` ` `2, 7, 0, 6, 0, 9);` `$n` `= sizeof(` `$arr` `);` `pushZerosToEnd(` `$arr` `, ` `$n` `);` `echo` `"Array after pushing all "` `.` ` ` `"zeros to end of array :\n"` `;` `for` `(` `$i` `= 0; ` `$i` `< ` `$n` `; ` `$i` `++)` `echo` `$arr` `[` `$i` `] . ` `" "` `;` `// This code is contributed` `// by ChitraNayal` `?>` |

## Javascript

`<script>` `// A JavaScript program to move all zeroes at the end of array` `// Function which pushes all zeros to end of an array.` `function` `pushZerosToEnd(arr, n)` `{` ` ` `let count = 0; ` `// Count of non-zero elements` ` ` `// Traverse the array. If element encountered is non-` ` ` `// zero, then replace the element at index 'count'` ` ` `// with this element` ` ` `for` `(let i = 0; i < n; i++)` ` ` `if` `(arr[i] != 0)` ` ` `arr[count++] = arr[i]; ` `// here count is` ` ` `// incremented` ` ` `// Now all non-zero elements have been shifted to` ` ` `// front and 'count' is set as index of first 0.` ` ` `// Make all elements 0 from count to end.` ` ` `while` `(count < n)` ` ` `arr[count++] = 0;` `}` `// Driver code` ` ` `let arr = [1, 9, 8, 4, 0, 0, 2, 7, 0, 6, 0, 9];` ` ` `let n = arr.length;` ` ` `pushZerosToEnd(arr, n);` ` ` `document.write(` `"Array after pushing all zeros to end of array :<br>"` `);` ` ` `for` `(let i = 0; i < n; i++)` ` ` `document.write(arr[i] + ` `" "` `); ` `// This code is contributed by Surbhi Tyagi.` `</script>` |

**Output:**

Array after pushing all zeros to end of array : 1 9 8 4 2 7 6 9 0 0 0 0

**Time Complexity:** O(n) where n is number of elements in input array.**Auxiliary Space: **O(1)

This article is contributed by** ****Chandra Prakash**. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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