代码

#include <algorithm>

void mergesort(unsigned* arr, int lo, int hi){
    if(hi - lo < 2) return;
    int mi = (lo + hi) >> 1;
    mergesort(arr, lo, mi);
    mergesort(arr, mi, hi);
    int len_a = mi - lo, len_b = hi - mi, i = 0, j = 0, p = 0;
    auto A = new unsigned[len_a], B = arr + mi;
    for(int k = 0; k < len_a; k++){
        A[k] = arr[k+lo];
    }
    while((i < len_a) && (j < len_b))
        arr[lo + p++] = (A[i] <= B[j]) ? A[i++] : B[j++];
    while(i < len_a)
        arr[lo + p++] = A[i++];
}

void sort(unsigned *a, int n) {
	mergesort(a, 0, n);
}

评测结果