poj3928pingpong区间和

　　题意：给出n； n个人有n个不同的技能值  问 任取三个人 使得 中间那人的 技能值也在其他两人之间。

树状数组

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <climits>
#include <string>
#include <iostream>
#include <map>
#include <cstdlib>
#include <list>
#include <set>
#include <queue>
#include <stack>
#include <math.h>
using namespace std;

typedef long long LL;
const LL maxn = 100000 + 100;
LL Max;
LL c[maxn];
LL zuomin[maxn],youmin[maxn],zuomax[maxn],youmax[maxn];
LL lowbit(LL x)
{
    return x&(-x);
}

void update(LL x, LL add)
{
    while (x <= Max){
        c[x] += add;
        x += lowbit(x);
    }
}

LL ask(LL x)
{
    LL ans = 0;
    while (x > 0){
        ans += c[x];
        x -= lowbit(x);
    }
    return ans;
}

int main()
{
    LL n;
    LL a[maxn],Icase;
    cin>>Icase;
    while (Icase--){
        cin>>n;
        Max = -1;
        for (LL i = 1; i <= n; i++)
            cin >> a[i],Max = max(Max,a[i]);
        memset(c, 0, sizeof(c));
        for (LL i = 1; i <= n; i++){
            zuomin[i] = ask(a[i]); zuomax[i]= ask(Max) - ask(a[i]);
            update(a[i], 1);//边统计左边比他大和比他小的 ，边插
        }
        memset(c, 0, sizeof(c));
        for (LL i = n; i >= 1; i--){
            youmin[i] = ask(a[i]); youmax[i] = ask(Max) - ask(a[i]);
            update(a[i], 1);
        }
        LL ans = 0;
        for (LL i = 1; i <= n; i++){
            ans += zuomin[i] * youmax[i];
            ans += zuomax[i] * youmin[i];
        }
        cout << ans << endl;
    }
    return 0;
}

线段树

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <climits>
#include <string>
#include <iostream>
#include <map>
#include <cstdlib>
#include <list>
#include <set>
#include <queue>
#include <stack>
#include <math.h>
using namespace std;
typedef long long LL;
const int maxn = 100000 + 100;
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
int sum[maxn * 4];
int zuomin[maxn], youmin[maxn], zuomax[maxn], youmax[maxn];
void up(int rt)
{
    sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
}
void build(int l, int r, int rt)
{
    sum[rt] = 0;
    if (l == r) return;
    int mid = (l + r) >> 1;
    build(lson);
    build(rson);
}
void update(int pos, int add, int l, int r, int rt)
{
    if (l == r){
        sum[rt] = 1; return;
    }
    int mid = (l + r) >> 1;
    if (pos <= mid) update(pos, add, lson);
    else update(pos, add, rson);
    up(rt);
}

int ask(int L, int R, int l, int r, int rt)
{
    if (L <= l&&r <= R) return sum[rt];
    int mid = (l + r) >> 1;
    int ans = 0;
    if (L <= mid) ans += ask(L, R, lson);
    if (R > mid) ans += ask(L, R, rson);
    return ans;
}
int main()
{
    int Icase;
    int n, Max;
    int a[maxn];
    cin >> Icase;
    while (Icase--){
        cin >> n;
        Max = -1;
        for (int i = 1; i <= n; i++) scanf("%d", &a[i]), Max = max(Max, a[i]);
        build(1, Max, 1);
        for (int i = 1; i <= n; i++){
            zuomin[i] = ask(1,a[i],1,Max,1); zuomax[i] = ask(1,Max,1,Max,1) - ask(1,a[i],1,Max,1);
            update(a[i], 1,1,Max,1);
        }
        build(1, Max, 1);
        for (int i = n; i >= 1; i--){
            youmin[i] = ask(1,a[i],1,Max,1); youmax[i] = ask(1,Max,1,Max,1) - ask(1,a[i],1,Max,1);
            update(a[i], 1,1,Max,1);
        }
        LL ans = 0;
        for (int i = 1; i <= n; i++){
            ans += zuomin[i] * youmax[i];
            ans += zuomax[i] * youmin[i];
        }
        cout << ans << endl;

    }
    return 0;
}