UVa 1606 Amphiphilic Carbon Molecules——极角扫描

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

using namespace std;

const int maxn = 1010;

struct Node {
int x, y, col;
double rad;
bool operator < (const Node &node) {
return rad < node.rad;
}
}node[maxn], tnode[maxn];

bool cross(int x1, int y1, int x2, int y2) {
return (x1 * y2 - x2 * y1) >= 0;
}

int main()
{
int n;
while (scanf("%d", &n) == 1 && n) {
for (int i = 0; i < n; i++) {
scanf("%d %d %d", &node[i].x, &node[i].y, &node[i].col);
}
if (n <= 3) {
printf("%d\n", n); continue;
}
int ans = 0;
for (int i = 0; i < n; i++) {
int k = 0;
for (int j = 0; j < n; j++) {
if (j == i) continue;
tnode[k].x = node[j].x - node[i].x;
tnode[k].y = node[j].y - node[i].y;
tnode[k].col = node[j].col;
if (tnode[k].col) {
tnode[k].x = -tnode[k].x, tnode[k].y = -tnode[k].y;
}
tnode[k].rad = atan2(tnode[k].y, tnode[k].x);
k++;
}
sort(tnode, tnode + k);
int L = 0, R = 0, cnt = 1;
while (L < k) {
if (R == L) {
R = (R + 1) % k;
cnt++;
}
while (R != L && cross(tnode[L].x, tnode[L].y, tnode[R].x, tnode[R].y)) {
R = (R + 1) % k;
cnt++;
}
ans = max(ans, cnt);
L++, cnt--;
}
}
printf("%d\n", ans);
}
return 0;
}