归并排序求逆序对的代码(C语言)

#include <stdio.h>
#include <stdlib.h>

#define MAX 32767

int merge(int *array, int p,int q,int r) { 
	//归并array[p...q] 与 array[q+1...r]

	int tempSum=0;
	int n1 = q-p+1;
	int n2 = r-q;
	int* left = NULL;
	int* right = NULL;
	int i,j,k;

	left = ( int *)malloc(sizeof(int) * (n1+1));
	right = ( int *)malloc(sizeof(int) * (n2+1));
	
	for(i=0; i<n1; i++)
		left[i] = array[p+i];

	for(j=0; j<n2; j++)
		right[j] = array[q+1+j];

	left[n1] = MAX; //哨兵，避免检查每一部分是否为空
	right[n2] = MAX;

	i=0;
	j=0;

	for(k=p; k<=r; k++) {
		if( left[i] <= right[j]) {
			array[k] = left[i];
			i++;
		} else {
			array[k] = right[j];
			j++;
			tempSum += n1 - i;
			printf("tempSum = %d\n", tempSum);
		}
	}
	return tempSum;

}

int mergeSort(int *array, int start, int end ) {
	int sum=0;
	if(start < end) {
		int mid = (start + end) /2;
		sum += mergeSort(array, start, mid);
		sum += mergeSort(array, mid+1, end);
		sum += merge(array,start,mid,end);
	}
	return sum;
}

int main(int argc, char** argv) {
	int array[5] = {9,1,0,5,4};
	int inversePairNum;
	int i;

	inversePairNum = mergeSort(array,0,4);
	for( i=0; i<5; i++)
		printf("%d ", array[i]);
	printf("\nInverse pair num = %d\n", inversePairNum);
	return 0;
}

 

    for(k=p; k<=r; k++) { 
        if( left[i] <= right[j]) { 
            array[k] = left[i]; 
            i++; 
        } else { 
            array[k] = right[j]; 
            j++; 
            tempSum += n1 - i; 
            printf("tempSum = %d\n", tempSum); 
        } 
    } 

    这部分是重点，思想是在合并left[0...n1] 和 right[0...n2]时，如果left[i] > right[j] ，则left 数组中第i个元素及后面的元素都将跟 right[j]构成逆序对，所以 tempSum += n1-i;

忘了free掉malloc的内存了
    free(left);
    free(right);
    left = NULL;
    right = NULL;