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51 lines (47 loc) · 846 Bytes
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Copy pathmerge_sort.c
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51 lines (47 loc) · 846 Bytes
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#include <stdio.h>
#include <stdlib.h>
/*merge sort and count reverses in the orignal array*/
int res = 0;
int merge(int *a, int l, int m, int r) {
int *b = (int*)malloc((r-l+1)*sizeof(int));
int k = 0;
int i, j;
i = l;
j = m+1;
while(i<=m && j<=r) {
if(a[i] <= a[j])
b[k++] = a[i++];
else {
b[k++] = a[j++];
res += m-i+1;
}
}
while(i <= m)
b[k++] = a[i++];
while(j <= r)
b[k++] = a[j++];
for(k=0; k<r-l+1; k++)
a[l+k] = b[k];
free(b);
}
void merge_sort(int *a, int l, int r) {
if(l >= r) {
return;
}
int m = (l+r)/2;
merge_sort(a, l, m);
merge_sort(a, m+1, r);
merge(a, l, m, r);
}
int main(void) {
int a[] = {10, 102, 9, 92};
int n = sizeof(a)/sizeof(a[0]);
merge_sort(a, 0, n-1);
int i;
for(i=0; i<n; i++) {
printf("%d ", a[i]);
}
printf("\n");
printf("res = %d\n", res);
return 0;
}