【POJ2187】Beauty Contest【旋转卡壳】

来源：互联网发布：迈普1800抹除数据编辑：程序博客网时间：2024/04/29 05:19

【题目链接】

学习一发旋转卡壳。

/* Telekinetic Forest Guard */#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int maxn = 50005;int n, m;struct Vector {int x, y;Vector(int a = 0, int b = 0) {x = a; y = b;}bool operator < (const Vector &a) const {return x != a.x ? x < a.x : y < a.y;}Vector operator - (const Vector &a) {return Vector(x - a.x, y - a.y);}} p[maxn], cov[maxn];inline int cross(Vector a, Vector b) {return a.x * b.y - a.y * b.x;}inline int dis(Vector a, Vector b) {return (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);}inline void Andrew() {sort(p + 1, p + 1 + n);m = 0;for(int i = 1, k = 1; i <= n; i++) {for(; m > k && cross(cov[m] - cov[m - 1], p[i] - cov[m - 1]) <= 0; m--);cov[++m] = p[i];}for(int i = n - 1, k = m; i; i--) {for(; m > k && cross(cov[m] - cov[m - 1], p[i] - cov[m - 1]) <= 0; m--);cov[++m] = p[i];}if(n > 1) m--;}inline int rotcov() {int res = 0;for(int i = 1, j = 2; i <= m; i++) {for(; cross(cov[i + 1] - cov[i], cov[j] - cov[i]) < cross(cov[i + 1] - cov[i], cov[j + 1] - cov[i]); j == m ? j = 1 : j++);res = max(res, max(dis(cov[i], cov[j]), dis(cov[i + 1], cov[j + 1])));}return res;}int main() {scanf("%d", &n);for(int i = 1; i <= n; i++) scanf("%d%d", &p[i].x, &p[i].y);Andrew();printf("%d\n", rotcov());return 0;}

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