mirror of https://github.com/TheAlgorithms/C
121 lines
2.1 KiB
C
121 lines
2.1 KiB
C
/**
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* @file
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* @brief Implementation of [merge
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* sort](https://en.wikipedia.org/wiki/Merge_sort) algorithm
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*/
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#include <stdio.h>
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#include <stdlib.h>
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/**
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* @addtogroup sorting Sorting algorithms
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* @{
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*/
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/** Swap two integer variables
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* @param [in,out] a pointer to first variable
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* @param [in,out] b pointer to second variable
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*/
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void swap(int *a, int *b)
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{
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int t;
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t = *a;
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*a = *b;
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*b = t;
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}
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/**
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* @brief Perform merge of segments.
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*
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* @param a array to sort
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* @param l left index for merge
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* @param r right index for merge
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* @param n total number of elements in the array
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*/
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void merge(int *a, int l, int r, int n)
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{
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int *b = (int *)malloc(n * sizeof(int)); /* dynamic memory must be freed */
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int c = l;
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int p1, p2;
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p1 = l;
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p2 = ((l + r) / 2) + 1;
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while ((p1 < ((l + r) / 2) + 1) && (p2 < r + 1))
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{
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if (a[p1] <= a[p2])
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{
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b[c++] = a[p1];
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p1++;
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}
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else
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{
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b[c++] = a[p2];
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p2++;
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}
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}
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if (p2 == r + 1)
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{
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while ((p1 < ((l + r) / 2) + 1))
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{
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b[c++] = a[p1];
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p1++;
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}
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}
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else
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{
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while ((p2 < r + 1))
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{
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b[c++] = a[p2];
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p2++;
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}
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}
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for (c = l; c < r - l + 1; c++) a[c] = b[c];
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free(b);
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}
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/** Merge sort algorithm implementation
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* @param a array to sort
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* @param n number of elements in the array
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* @param l index to sort from
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* @param r index to sort till
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*/
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void merge_sort(int *a, int n, int l, int r)
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{
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if (r - l == 1)
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{
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if (a[l] > a[r])
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swap(&a[l], &a[r]);
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}
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else if (l != r)
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{
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merge_sort(a, n, l, (l + r) / 2);
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merge_sort(a, n, ((l + r) / 2) + 1, r);
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merge(a, l, r, n);
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}
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/* no change if l == r */
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}
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/** @} */
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/** Main function */
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int main(void)
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{
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int *a, n, i;
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scanf("%d", &n);
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a = (int *)malloc(n * sizeof(int));
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for (i = 0; i < n; i++)
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{
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scanf("%d", &a[i]);
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}
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merge_sort(a, n, 0, n - 1);
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for (i = 0; i < n; i++)
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{
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printf(" %d", a[i]);
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}
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free(a);
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return 0;
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}
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