基本算法-归并排序

归并排序：是一种较稳定的排序算法
时间复杂度：nlogn
基本思想：将一个数组进行拆分成两两一组，然后分别对每组进行排序组合。
基本算法：

//将有二个有序数列a[first...mid]和a[mid...last]合并。void mergearray(int a[], int first, int mid, int last, int temp[]){    int i = first, j = mid + 1;    int m = mid,   n = last;    int k = 0;    while (i <= m && j <= n)    {        if (a[i] <= a[j])            temp[k++] = a[i++];        else            temp[k++] = a[j++];    }    while (i <= m)        temp[k++] = a[i++];    while (j <= n)        temp[k++] = a[j++];    for (i = 0; i < k; i++)        a[first + i] = temp[i];}void mergesort(int a[], int first, int last, int temp[]){    if (first < last)    {        int mid = (first + last) / 2;        mergesort(a, first, mid, temp);    //左边有序        mergesort(a, mid + 1, last, temp); //右边有序        mergearray(a, first, mid, last, temp); //再将二个有序数列合并    }}bool MergeSort(int a[], int n){    int *p = new int[n];    if (p == NULL)        return false;    mergesort(a, 0, n - 1, p);    delete[] p;    return true;}