uva 1428 - Ping pong(树状数组)

1a_i100000

Output

For each test case, output a single line contains an integer, the total number of different games.

Sample Input

1
3 1 2 3

Sample Output

1

以前没用过树状数组，都是用线段树的，不过既然碰到了这个典型例题，就还是自己手敲一遍吧，树状数组代码确实简单许多。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
using namespace std;
const int INF = 1000000000;
const int maxn = 100000 + 5;
typedef long long LL;

int a[maxn],c[maxn];
LL S_left[maxn],B_left[maxn];
int n;

int lowbit(int x){return x&-x;}

LL sum(int x){
    LL ret = 0;
    while(x > 0){
        ret += c[x];
        x -= lowbit(x);
    }
    return ret;
}

void add(int x){
    while(x <= maxn){
        c[x] += 1;
        x += lowbit(x);
    }
}

int main(){
    int t,Max;
    scanf("%d",&t);
    while(t--){
        Max = -1; 
        memset(c,0,sizeof(c));
        scanf("%d",&n);
        for(int i = 1;i <= n;i++){
            scanf("%d",&a[i]);
            add(a[i]);
            Max = max(Max,a[i]);
            S_left[i] = sum(a[i]-1);
            B_left[i] = max((LL)0,sum(Max)-sum(a[i]));
        }
        LL ans = 0;
        for(int i = 1;i <= n;i++){
            if(i == 1 || i == n) continue;
            ans += S_left[i] * ((sum(Max)-sum(a[i]))-B_left[i]);
            ans += B_left[i] * (sum(a[i]-1)-S_left[i]);
        }
        printf("%lld\n",ans);
    }
    return 0;
}