关于归并排序中内存释放的问题

[你还真行2012]

尝试了一个归并排序的例子，代码如下

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

void Merge(int a[], int p, int q, int r)
{
	int lenl = q - p+1;
	int lenr = r - q;
	
	int i, j,k;
	int *L = (int*)malloc(sizeof(lenl));
	int *R = (int*)malloc(sizeof(lenr));
	
	for (i = 0; i < lenl; i++) {
		L[i] = a[p + i];
	}
	
	for (j = 0; j < lenr; j++) {
		R[j] = a[q + 1 + j];
	}
	
	i = j = k = 0;
	while (i < lenl && j < lenr) {
		if (L[i]<R[j]) {
			a[p + k++] = L[i++];
		}
		else {
			a[p + k++] = R[j++];
		}
	}
	while (i < lenl) {
		a[p + k++] = L[i++];
	}
	while (j < lenr) {
		a[p + k++] = R[j++];
	}
	
	free(L);
	free(R);
}

void MergeSort(int a[], int p, int r)
{
	if (p == r) {
		return;
	}
	int mid = (p + r) / 2;
	MergeSort(a, p, mid);
	MergeSort(a, mid + 1, r);
	Merge(a, p, mid, r);
}

int main(void)
{
    int i;
	int a[] = { 76,5,34,3,13,4,6,75 };
	int last_index = sizeof(a) / sizeof(int) - 1;
	MergeSort(a, 0, last_index);
	for (i = 0; i <= last_index;i++) {
		printf("%d\n", a[i]);
	}
	return 0;
}

问题是在方法Merge中的最后两行代码free(L)和free(R)，加上这两句会运行错误，删掉会正常运行

[小灸舞]

是你malloc的地方有问题，应该是：
int *L = (int*)malloc(sizeof(int)*lenl);
int *R = (int*)malloc(sizeof(int)*lenr);

#include <stdio.h>
#include <stdlib.h>
 
void Merge(int a[], int p, int q, int r)
{
    int lenl = q - p+1;
    int lenr = r - q;
     
    int i, j,k;
    int *L = (int*)malloc(sizeof(int)*lenl);
    int *R = (int*)malloc(sizeof(int)*lenr);
     
    for (i = 0; i < lenl; i++) {
        L[i] = a[p + i];
    }
     
    for (j = 0; j < lenr; j++) {
        R[j] = a[q + 1 + j];
    }
     
    i = j = k = 0;
    while (i < lenl && j < lenr) {
        if (L[i]<R[j]) {
            a[p + k++] = L[i++];
        }
        else {
            a[p + k++] = R[j++];
        }
    }
    while (i < lenl) {
        a[p + k++] = L[i++];
    }
    while (j < lenr) {
        a[p + k++] = R[j++];
    }
     
    free(L);
    free(R);
}
 
void MergeSort(int a[], int p, int r)
{
    if (p == r) {
        return;
    }
    int mid = (p + r) / 2;
    MergeSort(a, p, mid);
    MergeSort(a, mid + 1, r);
    Merge(a, p, mid, r);
}
 
int main(void)
{
    int i;
    int a[] = { 76,5,34,3,13,4,6,75 };
    int last_index = sizeof(a) / sizeof(int) - 1;
    MergeSort(a, 0, last_index);
    for (i = 0; i <= last_index;i++) {
        printf("%d\n", a[i]);
    }
    return 0;
}

[paschen]

通常是你访问申请到的内存越界了而导致堆破坏，在释放时就会出错