poj 3185 The Water Bowls (dfs)

#include<stdio.h>
int ans,a[22],f,step;
int judge()
{
    int i;
    for(i=1;i<=20;i++)
       if(a[i]==1)return 0;

    return 1;
}
void change(int x)
{
    a[x]=!a[x];
    if(x-1>=1)a[x-1]=!a[x-1];
    if(x+1<=20)a[x+1]=!a[x+1];
}
void dfs(int x,int num)
{


    if(step==num)
    {
        if(judge())
        {
             f=1;

        }
         return ;

    }
    if(f||x>20)return ;
    change(x);
    dfs(x+1,num+1);//反转
    change(x);
    dfs(x+1,num);//不反转
}
int main()
{
    int i;
    for(i=1;i<=20;i++)
    {
        scanf("%d",&a[i]);
    }
    ans=0;
    f=0;
    for(step=0;step<20;step++)
    {

        dfs(0,0);
         if(f)
         {

             ans=step;
             break;
         }
    }

    printf("%d\n",ans);
}