主席树板子

Posted 2022-12-28 hs-black

主席树

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
using namespace std;
const int N = 200500;
struct node
    int l, r, sum;
    #define l(x) tree[x].l
    #define r(x) tree[x].r
    #define sum(x) tree[x].sum
tree[N<<5];
int read(void) 
    int x = 0,f = 1;
    char c = getchar();
    while (!isdigit(c)) 
        if (c == '-') f = -1;
        c = getchar();
    
    while (isdigit(c)) 
        x = (x << 3) + (x << 1) + c - '0';
        c = getchar();
    
    return x * f;

int n, m, a[N], b[N];
int q, cnt, t[N];
int build(int l, int r) 
    int rt = ++cnt;
    sum(rt) = 0;
    int mid = (l + r) >> 1;
    if (l < r) 
        l(rt) = build(l, mid);
        r(rt) = build(mid + 1, r);
    
    return rt;

inline int update(int pre,int l,int r,int x) 
    int rt = ++cnt;
    l(rt) = l(pre), r(rt) = r(pre);
    sum(rt) = sum(pre) + 1;
    int mid = (l + r) >> 1;
    if (l < r) 
        if (x <= mid) l(rt) = update(l(pre), l, mid, x);
        else r(rt) = update(r(pre), mid + 1, r, x);
    
    return rt;

inline int query(int u,int v,int l,int r,int k) 
    if (l >= r) return l;
    int x = sum(l(v)) - sum(l(u));
    int mid = (l + r) >> 1;
    if (x >= k) return query(l(u), l(v), l, mid, k);
    else return query(r(u), r(v), mid + 1, r, k - x);

int main() 
    n = read(), q = read();
    for (int i = 1;i <= n; i++) b[i] = a[i] = read();
    sort(b + 1,b + n + 1);
    m = unique(b + 1,b + n + 1) - b - 1;
    t[0] = build(1, m);
    for (int i = 1;i <= n; i++) 
        int T = lower_bound(b + 1,b + m + 1, a[i]) - b;
        t[i] = update(t[i-1], 1, m, T);
    
    while (q--) 
        int x = read(), y = read(), z = read();
        printf ("%d\n", b[query(t[x-1], t[y], 1, m, z)]);
    
    return 0;