题目地址：http://acm.hdu.edu.cn/showproblem.php?pid=1175
思路：BFS或者DFS，wrong了，有时间改
AC代码：
#include<stdio.h>
#include<string.h>
int dir[4][2] = {{0,1},{1,0},{0,-1},{-1,0}};
int x1,y1,x2,y2,m,n,mark,l = 0;
int a[1010][1010],visit[1010][1010];
void dfs(int x3,int y3,int sum,int direction)
{
int i;
if(x3 < 1 || x3 > n || y3 < 1 || y3 > m || visit[x3][y3] == 1)
return;
if(mark)
return;
if(sum > 2)
return;
if(x3 == x2 && y3 == y2)
{
mark = 1;
return;
}
if(a[x3][y3] != 0)
return;
visit[x3][y3] = 1;
for(i=0; i<4; i++)
{
if(direction != i)
dfs(x3+dir[i][0],y3+dir[i][1],sum+1,i);
else
dfs(x3+dir[i][0],y3+dir[i][1],sum,i);
}
visit[x3][y3] = 0;
}
int main()
{
int i,j,q;
while(scanf("%d%d",&n,&m))
{
if( n == 0 && m == 0)
break;
for(i=1; i<=n; i++)
{
for(j=1; j<=m; j++)
{
scanf("%d",&a[i][j]);
}
}
scanf("%d",&q);
while(q--)
{
mark = 0;
memset(visit,0,sizeof(visit));
scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
if(a[x1][y1] == a[x2][y2] && a[x1][y1] != 0 && (x1 !=x2 || y1 != y2))//0表示空格，即使都是零，也不能消去
{
visit[x1][y1] = 1;
for(i=0; i<4; i++)
{
dfs(x1+dir[i][0],y1+dir[i][1],0,i);
}
}
if(mark == 1)
printf("YES\n");
else
printf("NO\n");
}
}
return 0;
}
错误代码：
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <stack>
#include <map>
#include <cstring>
#include <climits>
#include <cmath>
#include <cctype>
const int inf = 0x7f7f7f7f;//2139062143
typedef long long ll;
using namespace std;
int n,m;
int map1[1010][1010];
int visit[1010][1010];
int dir[4][2] = {{-1,0},{1,0},{0,-1},{0,1}};
int sx,sy,ex,ey;
bool flag;
bool judge(int x,int y)
{
if(x >= 1 && x <=n && y >=1 && y<=m && !visit[x][y])
return true;
return false;
}
void dfs(int x,int y,int sum,int direction)
{
//printf("%d %d %d %d\n",x,y,sum,direction);
if(flag)
return;
if(sum > 2)
return;
if(x == ex && y == ey)
{
flag = true;
return;
}
if(map1[x][y] != 0)
return;
for(int i=0; i<4; i++)
{
int newx = x + dir[i][0];
int newy = y + dir[i][1];
if(judge(newx,newy))
{
visit[newx][newy] = 1;
if(direction == i)
{
dfs(newx,newy,sum,i);
}
else
{
dfs(newx,newy,sum+1,i);
}
visit[newx][newy] = 0;
}
}
}
int main()
{
while(scanf("%d%d",&n,&m) != EOF)
{
for(int i=1; i<=n; i++)
{
for(int j=1; j<=m; j++)
{
scanf("%d",&map1[i][j]);
}
}
int q;
scanf("%d",&q);
for(int i=0; i<q; i++)
{
memset(visit,0,sizeof(visit));
scanf("%d%d%d%d",&sx,&sy,&ex,&ey);
if(map1[sx][sy] != map1[ex][ey] || (sx == ex && sy == ey) || (map1[sx][sy] == 0 && map1[ex][ey] == 0))
{
printf("NO\n");
continue;
}
flag = false;
visit[sx][sy] = 1;
for(int i=0; i<4; i++)
{
int newx = sx + dir[i][0];
int newy = sy + dir[i][1];
if(judge(newx,newy))
{
dfs(newx,newy,0,i);
}
}
if(flag)
{
printf("YES\n");
}
else
{
printf("NO\n");
}
}
}
return 0;
}
错误代码：
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <stack>
#include <map>
#include <cstring>
#include <climits>
#include <cmath>
#include <cctype>
const int inf = 0x7f7f7f7f;//2139062143
typedef long long ll;
using namespace std;
int map1[1010][1010];
int visit[1010][1010];
int dir[4][2] = {{-1,0},{1,0},{0,-1},{0,1}};
int sx,sy,ex,ey;
int n,m;
struct point
{
int x;
int y;
int dir;
};
bool judge(int x,int y)
{
if(x >=1 && x <= n && y >= 1 && y <= m && (map1[x][y] == 0 || (x == ex && y == ey)) && !visit[x][y])
return true;
return false;
}
void bfs()
{
queue<point> que;
point in,out;
in.x = sx;
in.y = sy;
in.dir = 0;
visit[sx][sy] = 1;
que.push(in);
while(!que.empty())
{
out = que.front();
que.pop();
for(int i=0; i<4; i++)
{
int newx = out.x + dir[i][0];
int newy = out.y + dir[i][1];
while(judge(newx,newy))
{
visit[newx][newy] = 1;
in.x = newx;
in.y = newy;
in.dir = out.dir + 1;
if(in.dir <= 2)
que.push(in);
if(in.x == ex && in.y == ey && in.dir <=3)
{
printf("YES\n");
return;
}
newx += dir[i][0];
newy += dir[i][1];
}
}
}
printf("NO\n");
}
int main()
{
while(scanf("%d%d",&n,&m))
{
if(n + m == 0)
break;
for(int i=1; i<=n; i++)
{
for(int j=1; j<=m; j++)
{
scanf("%d",&map1[i][j]);
}
}
int q;
scanf("%d",&q);
for(int i=1; i<=q; i++)
{
memset(visit,0,sizeof(visit));
scanf("%d%d%d%d",&sx,&sy,&ex,&ey);
if()
}
}
return 0;
}
