poj2104 区间第K大

题目链接:http://poj.org/problem?id=2104

题意：给你一串数让你求区间第k大。 

分析：主席树模板题， 详细解释看这儿：主席树介绍

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>

using namespace std;
const int maxn = 100000 + 100;
int n, m;  //n个数字 m次查询
int L[maxn<<6], R[maxn<<6], sum[maxn<<6];
int tot;
int a[maxn], T[maxn], Hash[maxn];

int build(int l, int r) {   //建一个空树
    int rt = ++tot;
    sum[rt] = 0;
    if(l < r) {
        int m = (l+r)/2;
        L[rt] = build(l, m);
        R[rt] = build(m+1, r);
    }
    return rt;
}

int update(int pre, int l, int r, int x) {
    int rt = ++tot;
    L[rt] = L[pre]; R[rt] = R[pre]; sum[rt] = sum[pre] + 1;
    if(l < r) {
        int m = (l + r) / 2;
        if(x <= m)   //去左子树
            L[rt] = update(L[pre], l, m, x);
        else
            R[rt] = update(R[pre], m+1, r, x);
    }
    return rt;
}

int query(int u, int v, int l, int r, int k) {
    if(l >= r) return l;
    int m = (l+r)/2;
    int num = sum[L[v]] - sum[L[u]];
    if(num >= k)
        return query(L[u], L[v], l, m, k);
    else
        return query(R[u], R[v], m+1, r, k-num);
}

int main() {
       scanf("%d%d", &n, &m);
        for(int i=1; i<=n; i++) {
            scanf("%d", &a[i]);
            Hash[i] = a[i];
        }
        sort(Hash+1, Hash+1+n);
        int d = unique(Hash+1, Hash+1+n) - Hash - 1;
        tot = 0;
        T[0] = build(1,  d);    //建一个空树
        for(int i=1; i<=n; i++) {
            int x = lower_bound(Hash+1, Hash+1+d, a[i]) - Hash;
            T[i] = update(T[i-1], 1, d, x);
        }
        while(m--) {
            int l, r, k;
            scanf("%d%d%d", &l, &r, &k);
            int x = query(T[l-1], T[r], 1, d, k);
            printf("%d\n", Hash[x]);
        }
    return 0;
}


//7 3
//1 5 2 6 3 7 4
//2 5 3
//4 4 1
//1 7 3

//5
//6
//3