Hdu 5091 Beam Cannon (line segment tree scanning line), hdu5091

Hdu 5091 Beam Cannon (line segment tree scanning line), hdu5091

Link: hdu 5091 Beam Cannon

Given N vertices, we need to have a rectangle W ∗ H and ask how many vertices can be enclosed at most.

Solution: the scanning line of a line segment, assuming a bit (x, y), then (x, y )~ A rectangle (x + W, y + H) can be enclosed in the lower right corner of the frame (x, y)

Point, so N points are N rectangles. Find the maximum number of times of coverage and scan the line bare question.

#include <cstdio>#include <cstring>#include <vector>#include <algorithm>using namespace std;const int maxn = 40005;const int bw = 20000;#define lson(x) ((x)<<1)#define rson(x) (((x)<<1)|1)int lc[maxn << 2], rc[maxn << 2], ad[maxn << 2], nd[maxn << 2];inline void pushup(int u) {    nd[u] = max(nd[lson(u)], + nd[rson(u)]) + ad[u];}inline void maintain(int u, int v) {    ad[u] += v;    nd[u] += v;}void build(int u, int l, int r) {    lc[u] = l;    rc[u] = r;    ad[u] = nd[u] = 0;    if (l == r)        return;    int mid = (l + r) >> 1;    build(lson(u), l, mid);    build(rson(u), mid + 1, r);    pushup(u);}void modify(int u, int l, int r, int v) {    if (l <= lc[u] && rc[u] <= r) {        maintain(u, v);        return;    }    int mid = (lc[u] + rc[u]) >> 1;    if (l <= mid)        modify(lson(u), l, r, v);    if (r > mid)        modify(rson(u), l, r, v);    pushup(u);}int query(int u, int l, int r) {    if (l <= lc[u] && rc[u] <= r)        return nd[u];    int mid = (lc[u] + rc[u]) >> 1, ret = 0;     if (l <= mid)        ret = max(ret, query(lson(u), l, r));    if (r > mid)        ret = max(ret, query(rson(u), l, r));    pushup(u);    return ret;}struct Seg {    int x, l, r, w;    Seg(int x = 0, int l = 0, int r = 0, int w = 0) {        this->x = x;        this->l = l;        this->r = r;        this->w = w;    }};vector<Seg> G;inline bool cmp (const Seg& a, const Seg& b) {    if (a.x != b.x)        return a.x < b.x;    return a.w < b.w;}int N, W, H;void init () {    int x, y;    G.clear();    scanf("%d%d", &W, &H);    for (int i = 0; i < N; i++) {        scanf("%d%d", &x, &y);        G.push_back(Seg(x, y + bw, min(bw, y + H) + bw, 1));        G.push_back(Seg(x + W + 1, y + bw, min(bw, y + H) + bw, -1));    }    build(1, 0, bw * 2);    sort(G.begin(), G.end(), cmp);}int main () {    while (scanf("%d", &N) == 1 && N != -1) {        init();        int ans = 0;        for (int i = 0; i < G.size(); i++) {            modify(1, G[i].l, G[i].r, G[i].w);            ans = max(ans, nd[1]);        }        printf("%d\n", ans);    }    return 0;}