UVALive - 4329 Ping pong

Ping pong

Time Limit: 3000MS Memory Limit: Unknown 64bit IO Format: %lld & %llu

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Description

N(3N20000) ping pong players live along a west-east street(consider the street as a line segment). Each player has a unique skill rank. To improve their skill rank, they often compete with each other. If two players want to compete, they must choose a referee among other ping pong players and hold the game in the referee's house. For some reason, the contestants can't choose a referee whose skill rank is higher or lower than both of theirs. The contestants have to walk to the referee's house, and because they are lazy, they want to make their total walking distance no more than the distance between their houses. Of course all players live in different houses and the position of their houses are all different. If the referee or any of the two contestants is different, we call two games different. Now is the problem: how many different games can be held in this ping pong street?

Input

The first line of the input contains an integer T(1T20) , indicating the number of test cases, followed by T lines each of which describes a test case.

Every test case consists of N + 1 integers. The first integer is N , the number of players. Then N distinct integers a₁, a₂...a_N follow, indicating the skill rank of each player, in the order of west to east ( 1a_i100000 , i = 1...N ).

Output

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

Sample Input

13 1 2 3

Sample Output

1

Source

Regionals 2008 >> Asia - Beijing

分析：

树状数组题，好好体会这种思想。

ac代码：

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=20000+10;
const int maxnum=100000+10;
int n;
int a[maxn],b[maxn],temp[maxn];
int c[maxnum];


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


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


void add(int x,int d)
{
    while(x<=maxnum-1)//x<=n就wa了,因为是对1~maxnum进行枚举，不是对n进行枚举（n<=20000）
    {
        c[x]+=d;
        x+=lowbit(x);
    }
}


int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        for(int i=0;i<n;i++)
        scanf("%d",&temp[i]);
        memset(c,0,sizeof(c));
        for(int i=0;i<n;i++)
        {
            add(temp[i],1);
            a[i]=sum(temp[i])-1;//设x[c[i]]=1,所以减去一
        }
        memset(c,0,sizeof(c));
        for(int i=n-1;i>=0;i--)//从后向前修改，注意体会
        {
            add(temp[i],1);
            b[i]=sum(temp[i])-1;
        }
        long long ans=0;
        for(int i=1;i<n-1;i++)
        ans+=a[i]*(n-(i+1)-b[i])+(i+1-a[i]-1)*b[i];
        printf("%lld\n",ans);
    }
    return 0;
}