第六章 递归和分治法

1、Aizu ALDS1_5_A Exhaustive Search

#include<iostream>
using namespace std;
int a[30],n,m;
bool judge(int now,int val){
    if(val==0) return true;
    if(now==0){
        if(val==a[now])
            return true;
        return false;
    }
    if(judge(now-1,val)) return true;
    if(judge(now-1,val-a[now]))return true;
    return false;
}
int main ()
{
    int val;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    cin>>m;
    for(int i=0;i<m;i++){
         cin>>val;
         if(judge(n,val))
            cout<<"yes"<<endl;
         else
            cout<<"no"<<endl;
    }
    return 0;
}

2、Aizu ALDS1_5_C Koch Curve

（里面用到    某一点绕另一点逆时针旋转后的坐标公式，如下图）

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
using namespace std;
struct point{
    double x,y;
};
void print(point a){
    printf("%.8f %.8f\n",a.x,a.y);
}
void Koch(int cnt,point a,point b)
{
    if(cnt==0) return ;
    point d1,d2,mid;
    d1.x=a.x+(b.x-a.x)/3;
    d1.y=a.y+(b.y-a.y)/3;
    d2.x=a.x+2*(b.x-a.x)/3;
    d2.y=a.y+2*(b.y-a.y)/3;
    mid.x=d1.x+(d2.x-d1.x)*(cos(M_PI*60/180))-(d2.y-d1.y)*(sin(M_PI*60/180));
    mid.y=d1.y+(d2.x-d1.x)*(sin(M_PI*60/180))+(d2.y-d1.y)*(cos(M_PI*60/180));
    Koch(cnt-1,a,d1);
    print(d1);
    Koch(cnt-1,d1,mid);
    print(mid);
    Koch(cnt-1,mid,d2);
    print(d2);
    Koch(cnt-1,d2,b);
    return ;
}
int main ()
{
    int n;
    cin>>n;
    point a,b;
    a.x=0,a.y=0;
    b.x=100,b.y=0;
    print(a);
    Koch(n,a,b);
    print(b);
    return 0;
}