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# C Program for Merge Sort

• Difficulty Level : Easy
• Last Updated : 13 Feb, 2018

Merge Sort is a Divide and Conquer algorithm. It divides input array in two halves, calls itself for the two halves and then merges the two sorted halves. The merge() function is used for merging two halves. The merge(arr, l, m, r) is key process that assumes that arr[l..m] and arr[m+1..r] are sorted and merges the two sorted sub-arrays into one.

## C/C++

 `/* C program for Merge Sort */``#include``#include`` ` `// Merges two subarrays of arr[].``// First subarray is arr[l..m]``// Second subarray is arr[m+1..r]``void` `merge(``int` `arr[], ``int` `l, ``int` `m, ``int` `r)``{``    ``int` `i, j, k;``    ``int` `n1 = m - l + 1;``    ``int` `n2 =  r - m;`` ` `    ``/* create temp arrays */``    ``int` `L[n1], R[n2];`` ` `    ``/* Copy data to temp arrays L[] and R[] */``    ``for` `(i = 0; i < n1; i++)``        ``L[i] = arr[l + i];``    ``for` `(j = 0; j < n2; j++)``        ``R[j] = arr[m + 1+ j];`` ` `    ``/* Merge the temp arrays back into arr[l..r]*/``    ``i = 0; ``// Initial index of first subarray``    ``j = 0; ``// Initial index of second subarray``    ``k = l; ``// Initial index of merged subarray``    ``while` `(i < n1 && j < n2)``    ``{``        ``if` `(L[i] <= R[j])``        ``{``            ``arr[k] = L[i];``            ``i++;``        ``}``        ``else``        ``{``            ``arr[k] = R[j];``            ``j++;``        ``}``        ``k++;``    ``}`` ` `    ``/* Copy the remaining elements of L[], if there``       ``are any */``    ``while` `(i < n1)``    ``{``        ``arr[k] = L[i];``        ``i++;``        ``k++;``    ``}`` ` `    ``/* Copy the remaining elements of R[], if there``       ``are any */``    ``while` `(j < n2)``    ``{``        ``arr[k] = R[j];``        ``j++;``        ``k++;``    ``}``}`` ` `/* l is for left index and r is right index of the``   ``sub-array of arr to be sorted */``void` `mergeSort(``int` `arr[], ``int` `l, ``int` `r)``{``    ``if` `(l < r)``    ``{``        ``// Same as (l+r)/2, but avoids overflow for``        ``// large l and h``        ``int` `m = l+(r-l)/2;`` ` `        ``// Sort first and second halves``        ``mergeSort(arr, l, m);``        ``mergeSort(arr, m+1, r);`` ` `        ``merge(arr, l, m, r);``    ``}``}`` ` `/* UTILITY FUNCTIONS */``/* Function to print an array */``void` `printArray(``int` `A[], ``int` `size)``{``    ``int` `i;``    ``for` `(i=0; i < size; i++)``        ``printf``(``"%d "``, A[i]);``    ``printf``(``"\n"``);``}`` ` `/* Driver program to test above functions */``int` `main()``{``    ``int` `arr[] = {12, 11, 13, 5, 6, 7};``    ``int` `arr_size = ``sizeof``(arr)/``sizeof``(arr);`` ` `    ``printf``(``"Given array is \n"``);``    ``printArray(arr, arr_size);`` ` `    ``mergeSort(arr, 0, arr_size - 1);`` ` `    ``printf``(``"\nSorted array is \n"``);``    ``printArray(arr, arr_size);``    ``return` `0;``}`

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