HDU1394 Minimum Inversion Number 求逆序數

求逆序數，不解釋

#include <iostream>using namespace std;#define MAX 50005#include "NiXuShu.h"int main(){int a[MAX], b[MAX];int n, i;    while (scanf("%d", &n) == 1)    {memset(a, 0, sizeof(a));        int sum = 0;        for (int i = 1; i <= n; i ++){            scanf ("%d", &a[i]);//如果使用歸併排序來做，因為會改變數組的值，所以要另外開闢一個數組。//如果使用樹狀數組，則不需要這一步，直接調用b[i] = a[i];}        sum = NiXuShu(b, n+1);        int ans = sum;        for (int i = 1; i <= n; i++)        {            sum = sum - a[i] + (n - a[i] - 1);            ans = min(ans, sum);        }        printf("%d\n", ans);    }    return 0;}