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 + ;
 int n, m, cnt;
 struct node {
     int L, R, sum;
 } tree[maxn * ];
 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 = ;
     root[] = ;
     tree[].L = tree[].R = tree[].sum = ;
 }
 void updata(int num, int &rt, int l, int r) {
     tree[cnt++] = tree[rt];
     rt = cnt - ;
     tree[rt].sum++;
     if (l == r) return ;
     int mid = (l + r) >> ;
     if (num <= mid) updata(num, tree[rt].L, l, mid);
     else updata(num, tree[rt].R, mid + , 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) >> ;
     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 + , r) ;
 }
 int main() {
     scanf("%d%d", &n, &m);
     for (int i =  ; i <= n ; i++) {
         scanf("%d", &val[i].x);
         val[i].id = i;
     }
     sort(val + , val + n + , cmp);
     for (int i =  ; i <= n ; i++)
         RANK[val[i].id] = i;
     init();
     for (int i =  ; i <= n ; i++) {
         root[i] = root[i - ];
         updata(RANK[i], root[i], , n);
     }
     int left, right, k;
     for (int i =  ; i <= m ; i++) {
         scanf("%d%d%d", &left, &right, &k);
         printf("%d\n", val[query(root[left - ], root[right], k, , n)].x);
     }
     return ;
 }