题目链接:7-9 拯救007 (25 分)

AC代码:
代码中有注释

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>

using namespace std;

int n,d;
int vis[105];
bool flag;

struct Node{
	int x,y;
}nodes[105];

//判断007跳到第i个鳄鱼上时，再跳一步能否到达岸上 
bool lastJump(int i){
	if((nodes[i].x+d>=50)||(nodes[i].x-d<=-50)||(nodes[i].y+d>=50)||(nodes[i].y-d<=-50))
    {
    	return true;
	}
	return false;
}


//判断007能否从一个鳄鱼头上跳到另外一个鳄鱼头上
bool jumpSuccess(int a,int b){
	int x1 = pow(nodes[a].x-nodes[b].x,2);
    int x2 = pow(nodes[a].y-nodes[b].y,2);
    if(x1+x2<=d*d){
    	return true;
	}
	return false;
}

//判断007第一步能否跳到第一只鳄鱼上 
bool first(int t){
	int x1 = pow(nodes[t].x,2);
    int x2 = pow(nodes[t].y,2);
    
    if(x1+x2<=((d+7.5)*(d+7.5))) return true;
    return false;
} 


int dfs(int t){
	vis[t]=1;
	if(lastJump(t)){
		return flag=true; 
	}
  	
	for(int i=0;i<n;i++){
		if(!vis[i]&&jumpSuccess(t,i)){
			flag=dfs(i);
		}
	}
	return flag;
}

int main()
{
   scanf("%d%d",&n,&d);
   for(int i=0;i<n;i++)
   {
   	scanf("%d%d",&nodes[i].x,&nodes[i].y);
   }
   if(d>=42.5)
   {
   	printf("YES\n");
   }
   else{
   	  for(int i=0;i<n;i++)
	  {
   	      if(!vis[i]&&first(i)){
   	      	dfs(i);
		 }	
	  }
   	   if(flag){
   	   	printf("Yes\n");
		}
		else {
		  	printf("No\n");
		}
   }
   
	
   system("pause");
   return 0;
}