Solution for http://www.codeforces.com/contest/257/problem/C

view_angle.cpp

#include<iostream>
#include<cmath>
#include<algorithm>
#include<vector>
#include<cstdio>
using namespace std;

int main() {
	int n;
	cin >> n;

	vector<double> angles;

	int i, x, y;
	for(i = 0; i < n; i++) {
		cin >> x >> y;

		angles.push_back(atan2(y, x));
	}

	sort(angles.begin(), angles.end());

	double mx_diff = 0;
	for(i = 0; i < n-1; i++)
		mx_diff = max(mx_diff, angles[i+1]-angles[i]);

	double diff = angles[0]-angles[n-1];

	if(diff < 1e-7) diff += 360*M_PI/180;

	mx_diff = max(mx_diff, diff);

	printf("%.10lf\n", 360-(mx_diff*180/M_PI));
}