HDU 5091 Beam Cannon 线段树+扫描线

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;
struct edge_mode
{
int y, l, r, val;
void edge_make(int y,int l,int r,int val)
{
this->y = y;
this->l = l;
this->r = r;
this->val = val;
}
}edge[20005];
struct segment
{
int add, max;
}segtree[160005];
bool cmp(edge_mode a, edge_mode b)
{
if (a.y < b.y) return true;
else return false;
}
void init(int id, int l, int r)
{
segtree[id].add = segtree[id].max = 0;
if (l == r) return;
init(id << 1, l, (l + r) >> 1);
init(id << 1 | 1, ((l + r) >> 1 )+ 1, r);
}
void update(int id, int l, int r, int nl, int nr, int val)
{
if (r<nl || l>nr) return;
if (l >= nl&&r <= nr)
{
segtree[id].add += val;
segtree[id].max += val;
return;
}
update(id << 1, l, (l + r) >> 1, nl, nr, val);
update(id << 1 | 1, ((l + r) >> 1) + 1, r, nl, nr, val);
segtree[id].max = max(segtree[id << 1].max, segtree[id << 1 | 1].max) + segtree[id].add;
}
int main()
{
int n, w, h;
while ((scanf("%d %d %d", &n, &w, &h)) == 3)
{
init(1, 0, 40000);
for (int x = 0, y = 0, i = 0; i < n; i++)
{
scanf("%d %d", &x, &y);
x += 20000; y += 20000;
edge[2 * i].edge_make(y, x, x + w, 1);
edge[2 * i + 1].edge_make(y + h + 1, x, x + w, -1);
}
sort(edge, edge + 2 * n, cmp);
int ans = 0;
for (int i = 0,t = 0; i <= 40000; i++)
{
while (edge[t].y == i&&t < 2 * n)
{
update(1, 0, 40000, edge[t].l, edge[t].r, edge[t].val);
t++;
}
ans = max(ans, segtree[1].max);
}
printf("%d\n", ans);
}
return 0;
}