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mergesort.c
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mergesort.c
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//
// mergesort.c
//
// MIT licensed.
// Copyright (c) Abraham Hernandez <abraham@abranhe.com>
//
#include <string.h>
#include <stdlib.h>
// Merge the two half into a sorted data.
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);
}
}