HDU1728逃离迷宫(dfs+剪枝)
2018-02-28 23:59
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解题思路:一开始觉得是深搜模板题也没多想,结果WA,发现输入的出发点和终点都是先列再行(坑),改了下,又WA。起初的book数组我用来存结点是否走过,原来这里出bug了,题意是让我们找结点是否能在k次转弯内抵达。这里存在着可能这个结点上次搜超过k次了,但是我们把他标记走过,等到下次经过这却没超过k次,由于上次标记,我们也把他筛掉。这显然不正确,这是就改一下,book数组存到达本点的最小转弯数,就可以了。这种思路可以拓展到广搜,用优先队列,明天写下。
AC代码如下:
#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string.h>
#include<string>
#include<map>
#include<queue>
#include<stack>
#include<stdlib.h>
#include<math.h>
#define inf 0x3f3f3f3f
using namespace std;
char image[110][110];
int book[110][110],nex[4][2]={0,1,1,0,0,-1,-1,0},n,m,k,flag,tx,ty;
bool judge(int x,int y)
{
if(x<1 || x>n || y<1 || y>m || image[x][y]=='*')
return true;
return false;
}
void dfs(int x,int y,int bearing)
{
if(x==tx && y==ty)
{
if(book[x][y]<=k) flag=1;
return ;
}
int a,b,i;
for(i=0;i<4;i++)
{
a=x+nex[i][0];
b=y+nex[i][1];
if(judge(a,b) || book[a][b]<book[x][y])
continue;
if(i!=bearing && book[a][b]<book[x][y]+1)
continue;
book[a][b]=book[x][y];
if(i!=bearing) book[a][b]++;
if(book[a][b]>k || book[a][b]==k && (a!=tx && b!=ty))
continue;
dfs(a,b,i);
if(flag)
return ;
}
return ;
}
int main()
{
int t,i,j,x,y,a,b;
cin>>t;
while(t--)
{
scanf("%d%d",&n,&m);
getchar();
for(i=1;i<=n;i++)
{
scanf("%s",image[i]+1);
for(j=1;j<=m;j++)
book[i][j]=inf;
}
cin>>k>>y>>x>>ty>>tx;
if(y==ty && x==tx)
{
cout<<"yes"<<endl;
continue;
}
flag=0;
book[x][y]=0;
for(i=0;i<4 && !flag;i++)
{
a=x+nex[i][0];
b=y+nex[i][1];
if(judge(a,b))
continue;
book[a][b]=0;
dfs(a,b,i);
}
if(flag)
cout<<"yes"<<endl;
else
cout<<"no"<<endl;
}
return 0;
}
AC代码如下:
#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string.h>
#include<string>
#include<map>
#include<queue>
#include<stack>
#include<stdlib.h>
#include<math.h>
#define inf 0x3f3f3f3f
using namespace std;
char image[110][110];
int book[110][110],nex[4][2]={0,1,1,0,0,-1,-1,0},n,m,k,flag,tx,ty;
bool judge(int x,int y)
{
if(x<1 || x>n || y<1 || y>m || image[x][y]=='*')
return true;
return false;
}
void dfs(int x,int y,int bearing)
{
if(x==tx && y==ty)
{
if(book[x][y]<=k) flag=1;
return ;
}
int a,b,i;
for(i=0;i<4;i++)
{
a=x+nex[i][0];
b=y+nex[i][1];
if(judge(a,b) || book[a][b]<book[x][y])
continue;
if(i!=bearing && book[a][b]<book[x][y]+1)
continue;
book[a][b]=book[x][y];
if(i!=bearing) book[a][b]++;
if(book[a][b]>k || book[a][b]==k && (a!=tx && b!=ty))
continue;
dfs(a,b,i);
if(flag)
return ;
}
return ;
}
int main()
{
int t,i,j,x,y,a,b;
cin>>t;
while(t--)
{
scanf("%d%d",&n,&m);
getchar();
for(i=1;i<=n;i++)
{
scanf("%s",image[i]+1);
for(j=1;j<=m;j++)
book[i][j]=inf;
}
cin>>k>>y>>x>>ty>>tx;
if(y==ty && x==tx)
{
cout<<"yes"<<endl;
continue;
}
flag=0;
book[x][y]=0;
for(i=0;i<4 && !flag;i++)
{
a=x+nex[i][0];
b=y+nex[i][1];
if(judge(a,b))
continue;
book[a][b]=0;
dfs(a,b,i);
}
if(flag)
cout<<"yes"<<endl;
else
cout<<"no"<<endl;
}
return 0;
}
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