算法导论-归并排序

/*********************************************************************************************
归并排序
分治思想
递归
详见算法导论中文版page17
*********************************************************************************************/

#include <iostream>
using namespace std;
void merge(int[], int, int, int);
void merge_sort(int[], int, int);
int main() {

int testa[] = { 3,4,1,5,7,8,4,0,11,1 };
merge_sort(testa, 0, 9);
system("pause");

// 看看是否testa数组已经改变。函数调用改变了其值
for (int i = 0; i < 10; i++) {
cout << testa[i] << " ";
}
system("pause");
return 0;
}
void merge(int a[], int p, int q, int r) {
int n1, n2;
n1 = q - p + 1;		//from p to q
n2 = r - q;			// from q+1 to r
// c语言用malloc
int *L = (int*)malloc((n1+1)*sizeof(int));
int *R = (int*)malloc((n2+1)*sizeof(int));
for (int i = 0; i < n1; i++)
*(L+i) = a[p + i];
for (int j = 0; j < n2; j++) {
*(R+j) = a[q + 1 + j];
}
*(L + n1) = 1000;
*(R + n2) = 1000;
for (int k = p, i = 0, j = 0; k <= r; k++) {
if (*(L+i) <= *(R+j)) {
a[k] = *(L+i);
i++;
}
else {
a[k] = *(R+j);
j++;
}
}

free(L); free(R);
//每次输出排序子类，便于观察
for (int i = p; i <= r; i++) {
cout << a[i] << " ";
}
cout << endl;

}
void merge_sort(int a[], int p, int r) {
if (p < r) {
int q = (p + r) / 2;
merge_sort(a, p, q);
merge_sort(a, q + 1, r);
merge(a, p, q, r);
}
}