python/TangDou/AcWing/SegmentTree/HDU5091.cpp

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;
const int N = 40010;

struct Node {
    int l, r, lazy;
    int maxc;
} tr[N << 2];

struct Seg {
    int x, y1, y2, c;
    bool operator<(const Seg &t) const {
        if (x == t.x) return c > t.c;
        return x < t.x;
    }
} seg[N << 1];

void pushup(int u) {
    tr[u].maxc = max(tr[u << 1].maxc, tr[u << 1 | 1].maxc);
}

void pushdown(int u) {
    if (tr[u].lazy) {
        tr[u << 1].lazy += tr[u].lazy;
        tr[u << 1 | 1].lazy += tr[u].lazy;
        tr[u << 1].maxc += tr[u].lazy;
        tr[u << 1 | 1].maxc += tr[u].lazy;
        tr[u].lazy = 0;
    }
}
void build(int u, int l, int r) {
    tr[u] = {l, r, 0, 0};
    if (l == r) return;
    int mid = (l + r) >> 1;
    build(u << 1, l, mid);
    build(u << 1 | 1, mid + 1, r);
}

void modify(int u, int l, int r, int v) {
    if (l <= tr[u].l && tr[u].r <= r) {
        tr[u].lazy += v;
        tr[u].maxc += v;
        return;
    }
    pushdown(u);
    int mid = tr[u].l + tr[u].r >> 1;
    if (l <= mid) modify(u << 1, l, r, v);
    if (r > mid) modify(u << 1 | 1, l, r, v);
    pushup(u);
}

//离散化数组
vector<int> ys;

int find(int x) {
    return lower_bound(ys.begin(), ys.end(), x) - ys.begin();
}

int main() {
    //加快读入
    ios::sync_with_stdio(false), cin.tie(0);
    int n, w, h;
    while (cin >> n && ~n) {
        //多组数测数据
        memset(tr, 0, sizeof tr);
        ys.clear();
        int idx = 0;
        cin >> w >> h;
        for (int i = 1; i <= n; i++) {
            int x, y;
            cin >> x >> y;
            seg[++idx] = {x, y, y + h, 1};
            seg[++idx] = {x + w, y, y + h, -1};
            ys.push_back(y);
            ys.push_back(y + h);
        }

        //对于边，按x由小到大，入边在前，出边在后排序
        sort(seg + 1, seg + 1 + idx);

        //离散化=排序+ 去重
        sort(ys.begin(), ys.end());
        ys.erase(unique(ys.begin(), ys.end()), ys.end());

        //离散化似乎应该成为必要的步骤，这样记忆起来省的麻烦，都是一样的套路才方便记忆
        build(1, 0, ys.size() - 1); // 0~ys.size()-1,共 ys.size()个,线段树是建立在y轴的投影上

        int ans = 0;
        for (int i = 1; i <= idx; i++) {
            modify(1, find(seg[i].y1), find(seg[i].y2), seg[i].c);
            ans = max(ans, tr[1].maxc);
        }
        printf("%d\n", ans);
    }
    return 0;
}