K-th Closest Distance

题目链接

题意：n个数，q次查询，查询[l , r] 内， | a[i] - p | 第k大的数

思路：主席树维护下权值大小，二分答案，查询区间[p - mid, p + mid] 的个数

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<map>
#include<vector>
#include<queue>
#include<cmath>
using namespace std;
const int N = 1e5 + 10;
const int M = 1e6;
struct node {
    int l, r;
    int val;
}tree[N * 55];
int root[N], tot;
int n, q, a[N];
int update(int pre, int pl, int pr, int val) {
    int cur = ++tot;
    tree[cur] = tree[pre];
    tree[cur].val ++;
    if(pl == pr) return cur;
    int mid = (pl + pr) >> 1;
    if(val <= mid) tree[cur].l = update(tree[pre].l, pl, mid, val);
    else tree[cur].r = update(tree[pre].r, mid + 1, pr, val);
    return cur;
}
int k, cnt;
int query(int pl, int pr, int l, int r, int rt, int lt) {
    if(pl <= l && r <= pr) {
        return tree[rt].val - tree[lt].val;
    }
    int mid = (l + r) >> 1;
    int res = 0;
    if(pl <= mid) res += query(pl, pr, l, mid, tree[rt].l, tree[lt].l);
    if(pr > mid) res += query(pl, pr, mid + 1, r, tree[rt].r, tree[lt].r);
    return res;
}
int main( ) {
    int T, prex;
    int l, r, p;
    int pl, pr, mid;
    scanf("%d", &T);
    while(T--) {
        scanf("%d %d", &n, &q);
        for(int i = 1; i <= n; i++) {
            scanf("%d", &a[i]);
            root[i] = update(root[i - 1], 1, M, a[i]);
        }
        prex = 0;
        while(q--) {
            scanf("%d %d %d %d", &l, &r, &p, &k);
            l = l ^ prex; r = r ^ prex; p = p ^ prex; k = k ^ prex;
            pl = 0, pr = M;
            while(pl <= pr) {
                mid = (pl + pr) >> 1;
                if(query(max(1, p - mid), min(M, p + mid), 1, M, root[r], root[l - 1]) >= k) {
                    prex = mid;
                    pr = mid - 1;
                } else pl = mid + 1;
            }
            printf("%d
", prex);
        }
    }
    return 0;
}