AcWing 248. 窗内的星星

思路：

对于给定的点(星星)我们将他作为矩形的左下角

构造两条线段 seg左(x,y,y+h-1,c) seg右(x+w-1,y,y+h-1,-c)

然后线段树维护最大值

#include<bits/stdc++.h>
#include <unordered_map> 
using namespace std;
template<class...Args>
void debug(Args... args) {//Parameter pack 
    auto tmp = { (cout << args << ' ', 0)... };
    cout << "\n";
}
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll>pll;
typedef pair<int, int>pii;
const ll N = 2e5 + 5;
const ll INF = 0x7fffffff;
const ll MOD = 998244353;

struct segment {
    ll key, l, r;//记录每一条线
    ll k;//每一条线的权值(+1,-1)
    bool operator < (const segment& t) const {
        if (key == t.key)return k > t.k;
        return key < t.key;
    }
}seg[N << 1];
vector<ll> ys;//存储所有的y，用于离散化
ll get_pos(ll num) {
    return lower_bound(ys.begin(), ys.end(), num) - ys.begin() + 1;
}

struct Tree {
    struct node {
        ll l, r;
        ll maxv;//维护的是再w*h范围内的最大数
        ll add;//加法懒标记

    }tree[N << 2];
    void push_up(int root) {
        tree[root].maxv = max(tree[root << 1].maxv, tree[root << 1 | 1].maxv);
    }
    void build(int root, ll l, ll r) {
        if(l==r)tree[root] = { l, r, 0, 0 };
        else {
            tree[root] = { l,r };
            ll mid = l + r >> 1;
            build(root << 1, l, mid);
            build(root << 1 | 1, mid + 1, r);
        }
    }
    void push_down(int root) {
        if (tree[root].add) {
            tree[root << 1].add += tree[root].add;
            tree[root << 1 | 1].add += tree[root].add;
            tree[root << 1].maxv += tree[root].add;
            tree[root << 1 | 1].maxv += tree[root].add;
            tree[root].add = 0;
        }
    }
    void modify(int root, ll l, ll r, ll num) {
        if (l <= tree[root].l && tree[root].r <= r) {//节点包含在修改区间内部则直接修改
            tree[root].add += num;
            tree[root].maxv += num;
        }
        else {
            push_down(root);
            int mid = tree[root].l + tree[root].r >> 1;
            if (l <= mid)modify(root << 1, l, r, num);
            if (r > mid)modify(root << 1 | 1, l, r, num);
            push_up(root);
        }
    }
}tr;

int main() {
    ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    
    int n, w, h;
    while (cin >> n >> w >> h) {
        int pos = 0;
        for (int i = 0; i < n; i++) {
            ll x, y, c;
            cin >> x >> y >> c;
            ys.push_back(y);
            ys.push_back(y + h - 1);
            seg[pos++] = { x,y,y + h - 1,c };
            seg[pos++] = { x + w - 1,y,y + h - 1,-c };
        }
        sort(ys.begin(), ys.end());
        ys.erase(unique(ys.begin(), ys.end()), ys.end());

        ll ans = -1;
        tr.build(1, 1, ys.size());
        sort(seg, seg + 2 * n);
        for (int i = 0; i < 2 * n; i++) {
            ans = max(ans, tr.tree[1].maxv);
            ll l = get_pos(seg[i].l);
            ll r = get_pos(seg[i].r);
            tr.modify(1, l, r, seg[i].k);
        }
        cout << ans << "\n";
    }

    return 0;
}