【树状数组】HDOJ 2492 Ping pong

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简单的树状数组。枚举每一个裁判，ans=left_min[i]*right_max[i]+left_max[i]*right_min[i]。写的时候直接把n当成树状数组的最大值了，找了半天的错找吐血了。。。。。贴上代码。

#include <iostream>#include <sstream>#include <algorithm>#include <vector>#include <queue>#include <stack>#include <map>#include <set>#include <bitset>#include <cstdio>#include <cstring>#include <cstdlib>#include <cmath>#include <climits>#define maxn 100005#define eps 1e-7#define mod 1000000007#define INF 99999999#define lowbit(x) (x&(-x))typedef long long LL;using namespace std;int tree[maxn];int num[maxn];int left_min[maxn], left_max[maxn];int right_min[maxn], right_max[maxn];int n;void add(int x, int c){    for(int i=x;i<=maxn;i+=lowbit(i)) tree[i]+=c;}int sum(int x){    int i, ans=0;    for(i=x;i>0;i-=lowbit(i)) ans+=tree[i];    return ans;}void read(void){    int i;    scanf("%d",&n);    for(i=1;i<=n;i++) scanf("%d",&num[i]);    memset(left_min, 0, sizeof left_min);    memset(left_max, 0, sizeof left_max);    memset(right_min, 0, sizeof right_min);    memset(right_max, 0, sizeof right_max);}void solve(void){    int i;    memset(tree, 0, sizeof tree);    for(i=1;i<=n;i++){        left_min[i]=sum(num[i]);        left_max[i]=i-1-sum(num[i]-1);        add(num[i], 1);    }    memset(tree, 0, sizeof tree);    for(i=n;i>=1;i--){        right_min[i]=sum(num[i]);        right_max[i]=n-i-sum(num[i]-1);        add(num[i], 1);    }    LL ans=0;    for(i=1;i<=n;i++){        ans+=left_min[i]*right_max[i];        ans+=left_max[i]*right_min[i];    }    printf("%I64d\n", ans);}int main(void){    int _;    while(scanf("%d",&_)!=EOF){        while(_--){            read();            solve();        }    }}

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