HDU 5280 Lights

题目传送门
https://www.bilibili.com/video/BV1Tk4y1m7VM?p=23
没看懂，等功力够了，再来填坑吧

#include <iostream>
#include <cstdio>
#include <string>
#include <ctime>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <stack>
#include <climits>
#include <queue>
#include <map>
#include <set>
#include <sstream>
#include <cassert>

using namespace std;
typedef pair<int, int> PII;
#define x first
#define y second

const int N = 5e5 + 100;
const int M = 50000;

int prex[M], prey[M], n;

PII p[N];
/*主席树*/
struct Node {
    int l, r;
    int ls, rs;
    int sum;
} tr[N * 32];

int root[N], idx;

void insert(int &p, int l, int r, int x) {
    int q = idx++;
    tr[q] = tr[p];
    p = idx - 1;
    tr[p].sum++;
    if (l == r) return;
    int mid = (l + r) >> 1;
    if (x <= mid)
        insert(tr[p].l, l, mid, x);
    else
        insert(tr[p].r, mid + 1, r, x);
}

//左根，右根，当前区间，目标区间
int query(int i, int j, int l, int r, int L, int R) {
    if (r < L || l > R) return 0;                       //不在范围内，返回0
    if (l >= L && r <= R) return tr[j].sum - tr[i].sum; //计算前缀和的差
    int mid = (l + r) >> 1;
    return query(tr[i].l, tr[j].l, l, mid, L, R) + query(tr[i].r, tr[j].r, mid + 1, r, L, R);
}

/*主席树*/
bool solve() {
    memset(prex, 0, sizeof(prex));
    memset(prey, 0, sizeof(prey));
    memset(root, 0, sizeof root);

    //构建主席树的0号
    root[0] = 0;
    tr[0].l = tr[0].r = tr[0].sum = tr[0].ls = tr[0].rs = 0;
    idx = 1;

    int last = 0;
    for (int i = 1; i <= n; i++) {
        //如果相邻的结点坐标一样，不处理
        if (p[i].x == p[i - 1].x && p[i].y == p[i - 1].y) continue;
        //取出当前点坐标
        int x = p[i].x, y = p[i].y;

        int xx = p[prey[y]].x, yy = p[prex[x]].y;
        root[x] = root[last];

        insert(root[x], 1, M, y);

        if (query(root[xx], root[x], 1, M, yy + 1, y - 1)) return false;
        last = x, prex[x] = i, prey[y] = i;
    }
    return true;
}

int main() {
    //本题使用cin直接TLE，即使采用sync进行cin优化，依然也有时超时,只能采用scanf来读取
    while (~scanf("%d", &n) && n) {
        //每个路灯的坐标(x,y)
        for (int i = 1; i <= n; i++) scanf("%d%d", &p[i].x, &p[i].y);

        //主席树，一般都是要求排序的,这里是用x坐标为基准进行排序的
        sort(p + 1, p + 1 + n);
        bool flag = solve();

        //一正一反两次
        for (int i = 1; i <= n; i++) p[i].x = M - p[i].x;
        sort(p + 1, p + 1 + n);
        flag &= solve();

        if (flag)
            puts("YES");
        else
            puts("NO");
    }
    return 0;
}