C++之归并排序（7）---《那些奇怪的算法》

由于快速排序算法的最快时间复杂度为O(nlogn)，最慢为O(n^2)，因此就有大牛研究能不能将其时间复杂度降到恒定为O(nlogn)，于是归并排序就出现啦！

先划分，在归并，有些类似于快排：

#include <iostream>
using namespace std;

void merge(int A[], int left[], int leftCount, int right[], int rightCount){
int i = 0, j = 0, k = 0;
while (i < leftCount&&j < rightCount){
if (left[i] < right[j]){
A[k++] = left[i++];
}
else{
A[k++] = right[j++];
}
}
while (i < leftCount) A[k++] = left[i++];
while (j < leftCount) A[k++] = right[j++];
}
void mergeSort(int A[], int n){
int mid;
int *left, *right;
if (n < 2) return;
mid = n / 2;
left = new int[mid];
right = new int[n - mid];
for (int i = 0; i < mid; i++) left[i] = A[i];
for (int i = mid; i < n; i++) right[i - mid] = A[i];
mergeSort(left, mid);
mergeSort(right, n - mid);
merge(A, left, mid, right, n - mid);

delete[] left;
delete[] right;
}

int main(){
int A[] = { 10, 9, 1, 2, 6, 8, 7, 5, 3, 4 };
int len = sizeof(A) / sizeof(A[0]);
mergeSort(A, len);
for (int i = 0; i < len; i++){
cout << A[i] << " ";
}
cout << endl;
return 0;
}

运行结果：



参考：http://blog.csdn.net/a130737/article/details/38228369