排序算法之归并排序

归并思想是将问题分解为更小的、同性质的子问题，求解子问题，然后合并子问题的解得到原问题的解。经历一个分界、求解、合并的过程。因此上归并排序为将数组分为若干个子数组，分别排序，然后合并子数组的排序结果，即合并两个排序的数组，相关代码如下：

void MergeAubArray(int res[], int a[], int left, int mid, int right) //子数组以mid为界，下边为left~mid，mid+1 ~ right , res[] 为结果暂时存放的数组{    int left_a = left;    int left_b = mid + 1;    int k = left;    while (left_a <= mid && left_b <= right) { //子数组未合并完        if (a[left_a] < a[left_b]) {            res[k++] = a[left_a++];        }        else {            res[k++] = a[left_b++];        }    }    while (left_a <= mid) {  //a子数组未合并完，复制剩余元素        res[k++] = a[left_a++];    }    while (left_b <= right) { //b数组未合并完，赋值剩余元素        res[k++] = a[left_b++];    }    for (int i = left; i <= right; i++) {  //将合并结果赋值到原数组        a[i] = res[i];    }    return;}

归并排序算法：

void EX_SortMerge(int res[], int a[], int left, int right){    if (left >= right) {        return;    }    int mid = (right - left) / 2 + left;    EX_SortMerge(res, a, left, mid);    EX_SortMerge(res, a, mid + 1, right);    MergeAubArray(res, a, left, mid, right);    return;}