UVALive - 4329 Ping pong 数状数组

坑点：结果会爆int的范围。

传送门：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=13895

#include <cstdio>
#include <cstring>
#include <stack>
#include <queue>
#include <iostream>
#include <algorithm>
#include <map>
#include <vector>

using namespace std;

const long long MAXN = 100005;

long long Bit[MAXN<<1];
long long a[MAXN];
long long pre[MAXN];
long long eng[MAXN];

void Insert(long long x,long long value) {
    for(long long i = x ; i <= MAXN ; i += (i & -i)) {
        Bit[i] += value;
    }
} 

long long Query(long long x) {
    long long ret = 0;
    for(long long i = x ; i ; i -= (i & -i)) {
        ret += Bit[i];
    }
    return ret;
}

void Deal_with() {
    long long T,n;
    scanf("%lld",&T);
    while(T--) {
        scanf("%lld",&n);
        for(long long i = 1 ; i <= n ; i++) {
            scanf("%lld",a+i);
        }

        memset(Bit,0,sizeof(Bit));
        memset(pre,0,sizeof(pre));
        for(long long i = 1 ; i <= n ; i++) {
            pre[i] = Query(a[i]-1);
            Insert(a[i],1);
            //prlong longf("%d : %d\n",i,pre[i]);
        }
        //puts("");

        memset(Bit,0,sizeof(Bit));
        memset(eng,0,sizeof(eng));
        for(long long i = n; i >= 1 ;i --) { 
            eng[i] = Query(a[i]-1);
            Insert(a[i],1);
            //prlong longf("%d : %d\n",i,eng[i]);
        }

        long long ans = 0;
        for(long long i = 1 ; i <= n ; i++) {
            ans += pre[i] * (n - i - eng[i]);
            ans += (i - pre[i] - 1) * (eng[i]);
        }
        printf("%lld\n",ans);
    }
}

int main(void) {
    //freopen("a.in","r",stdin);
    Deal_with();
}