POJ 2104 K-th Number（主席树）

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <stack>
#include <bitset>
#include <cstdlib>
#include <cmath>
#include <set>
#include <list>
#include <deque>
#include <map>
#include <queue>
#define Max(a,b) ((a)>(b)?(a):(b))
#define Min(a,b) ((a)<(b)?(a):(b))
using namespace std;
typedef long long ll;
typedef long double ld;
const ld eps = 1e-9, PI = 3.1415926535897932384626433832795;
const int mod = 1000000000 + 7;
const int INF = 0x3f3f3f3f;
const int seed = 131;
const ll INF64 = ll(1e18);
const int maxn = 1e5 + 10;
int n,m,cnt,root[maxn],a[maxn],x,y,k;
struct node {
int l, r, sum;
}T[maxn * 40];
vector<int> v;
int getid(int x) { return lower_bound(v.begin(), v.end(), x) - v.begin() + 1; }
void update(int l, int r, int& x, int y, int pos) {
T[++cnt] = T[y];
T[cnt].sum++;
x = cnt;
if(l == r) return ;
int mid = (l + r) >> 1;
if(mid >= pos) update(l, mid, T[x].l, T[y].l, pos);
else update(mid+1, r, T[x].r, T[y].r, pos);
}
int query(int l, int r, int x, int y, int k) {
if(l == r) return l;
int mid = (l + r) >> 1;
int sum = T[T[y].l].sum - T[T[x].l].sum;
if(sum >= k) return query(l, mid, T[x].l, T[y].l, k);
else return query(mid+1, r, T[x].r, T[y].r, k - sum);
}
int main() {
while(~scanf("%d%d",&n,&m)) {
for(int i = 1; i <= n; i++) scanf("%d",&a[i]), v.push_back(a[i]);
sort(v.begin(), v.end()); v.erase(unique(v.begin(), v.end()), v.end());
for(int i = 1; i <= n; i++) update(1, n, root[i], root[i-1], getid(a[i]));
while(m--) {
scanf("%d%d%d",&x,&y,&k);
printf("%d\n", v[query(1, n, root[x-1],root[y], k)-1]);
}
}
return 0;
}