本文主要是介绍POJ Space Ant (向量夹角)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
http://poj.org/problem?id=1696
水。求出最大余弦值即可。
完整代码：
/*0ms,548KB*/#include<cstdio>
#include<cstring>
#include<cmath>double x[55], y[55], dx, dy;
bool vis[55];///单位化向量
inline void dentity_vector(double nowx, double nowy, double nextx, double nexty)
{double len = hypot(nextx - nowx, nexty - nowy);dx = (nextx - nowx) / len, dy = (nexty - nowy) / len;
}///i=(dx,dy),a=(x-nowx,y-nowy)
///注意向量i已经单位化
inline double getcos(double dx, double dy, double nowx, double nowy, double x, double y)
{return (dx * (x - nowx) + dy * (y - nowy)) / hypot(x - nowx, y - nowy);
}int main()
{int t, n, i, j, now, next;double miny, cos, tmp;scanf("%d", &t);while (t--){scanf("%d", &n);printf("%d", n);miny = 105;for (i = 1; i <= n; ++i){scanf("%*d%lf%lf", &x[i], &y[i]);if (y[i] < miny)miny = y[i], now = i;}memset(vis, 0, sizeof(vis));vis[now] = true;printf(" %d", now);dx = 1.0, dy = 0.0;for (i = 2; i <= n; ++i){cos = -1.0;for (j = 1; j <= n; ++j){if (!vis[j]){double tmp = getcos(dx, dy, x[now], y[now], x[j], y[j]);if (tmp > cos)cos = tmp, next = j;}}dentity_vector(x[now], y[now], x[next], y[next]);now = next;vis[now] = true;printf(" %d", now);}putchar(10);}return 0;
}
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