algorithm >> next_permutation

해당하는 구간의 순열을 알아서 만들어준다.

자세한것은
http://www.cplusplus.com/reference/algorithm/next_permutation/

내부구현은
http://stackoverflow.com/questions/11483060/stdnext-permutation-implementation-explanation
이런식이라고 한다.

next_permutation을 활용한 소스
https://www.acmicpc.net/problem/1007

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

struct Point{
    int x;
    int y;
    Point(){
        x=0;y=0;
    }
    Point(int _x, int _y){
        x=_x;
        y=_y;
    }

    Point operator + (Point p){
        Point ans;
        ans.x = x + p.x;
        ans.y = y + p.y;
        return ans;
    }

    Point operator - (Point p){
        Point ans;
        ans.x = x-p.x;
        ans.y = y-p.y;
        return ans;
    }

    void init(){
        x=0;
        y=0;
    }

    double scalar(){
        return sqrt((double)x*x+(double)y*y);
    }
};


void pointInit(Point point[]){
    for(int i=0;i<22;++i)point[i].init();
}

int main(){
    Point point[22];
    int n;
    int t;
    for(scanf("%d",&t);t;--t){
        pointInit(point);
        scanf("%d",&n);
        for(int i=0;i<n;++i){
            int x, y;
            scanf("%d%d",&x,&y);
            point[i].x=x;
            point[i].y=y;
        }
        vector<bool> v;
        for(int i=0;i<n/2;++i){
            v.push_back(true);
            v.push_back(false);
        }
        double ans = 98765432123;
        sort(v.begin(),v.end());
        do{
            Point p;
            for(int i=0;i<v.size();++i){
                if(v[i])p= p+point[i];
                else p =p-point[i];
            }
            ans = min(ans,p.scalar());
        }while(next_permutation(v.begin(),v.end()));

        printf("%.6lf\n",ans);
    }
}