HDU 5533 Dancing Stars on Me（凸包）

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题目大意

给出n个点，判断这n个点能否构成一个等边的严格凸包

分析

首先直接求凸包，判断是不是n个点全部用到了。
再依次比较每条边是否相等。

代码

#include <iostream>#include <cmath>#include <algorithm>using namespace std;const int maxn = 110;struct point {    int x , y;    bool operator < (point const &rhs) const {        return (x < rhs.x || (x == rhs.x && y < rhs.y));    }};point p[maxn] , ch[maxn];int cross(point const &O , point const &A , point const &B){    int xoa = A.x - O.x;    int yoa = A.y - O.y;    int xob = B.x - O.x;    int yob = B.y - O.y;    return xoa * yob - yoa * xob;}double dis(point A , point B){    return sqrt((double)(A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));}int ConvexHull(point *p , int n , point *ch){    sort(p , p + n);    int m = 0;    for(int i = 0; i < n; i++) {        while(m > 1 && cross(p[i] , ch[m-1] , ch[m-2]) < 0) m--;        ch[m++] = p[i];    }    int k = m;    for(int i = n - 2; i >= 0; i--) {        while(m > k && cross(p[i] , ch[m-1] , ch[m-2]) < 0) m--;        ch[m++] = p[i];    }    if(n > 1) m--;    return m;}int main(){    int t , n;    cin >> t;    while(t--)    {        cin >> n;        for(int i = 0; i < n; i++) cin >> p[i].x >> p[i].y;        int cnt = ConvexHull(p , n , ch);        if(cnt != n) cout << "NO" << endl;        else {            double d = dis(ch[0] , ch[1]);            int sign = 1;            for(int i = 2; i < n; i++) {                double tmp = dis(ch[i-1] , ch[i]);                if(tmp != d) {sign = 0; break;}            }            double tmp = dis(ch[0] , ch[n-1]);            if(tmp != d) sign = 0;            if(sign) cout << "YES" << endl;            else cout << "NO" << endl;        }    }    return 0;}

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