poj 2104 （主席树写法）

//求第K的的值


 1 #include<stdio.h>
#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
typedef long long LL;
const int maxn = 1e5 + 10;
int n, m, cnt;
struct node {
    int L, R, sum;
} tree[maxn * 20];
struct value {
    int x, id;
} val[maxn];
int cmp(value v1, value v2) {
    return v1.x < v2.x;
}
int root[maxn], RANK[maxn];
void init() {
    cnt = 1;
    root[0] = 0;
    tree[0].L = tree[0].R = tree[0].sum = 0;
}
void updata(int num, int &rt, int l, int r) {
    tree[cnt++] = tree[rt];
    rt = cnt - 1;
    tree[rt].sum++;
    if (l == r) return ;
    int mid = (l + r) >> 1;
    if (num <= mid) updata(num, tree[rt].L, l, mid);
    else updata(num, tree[rt].R, mid + 1, r);
}
int query(int i, int j, int k, int l, int r) {
    int d = tree[tree[j].L].sum - tree[tree[i].L].sum;
    if (l == r) return l;
    int mid = (l + r) >> 1;
    if (k <= d) return query(tree[i].L, tree[j].L, k, l, mid);
    else return query(tree[i].R, tree[j].R, k - d, mid + 1, r) ;
}
int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1 ; i <= n ; i++) {
        scanf("%d", &val[i].x);
        val[i].id = i;
    }
    sort(val + 1, val + n + 1, cmp);
    for (int i = 1 ; i <= n ; i++)
        RANK[val[i].id] = i;
    init();
    for (int i = 1 ; i <= n ; i++) {
        root[i] = root[i - 1];
        updata(RANK[i], root[i], 1, n);
    }
    int left, right, k;
    for (int i = 1 ; i <= m ; i++) {
        scanf("%d%d%d", &left, &right, &k);
        printf("%d\n", val[query(root[left - 1], root[right], k, 1, n)].x);
    }
    return 0;
}