萌新不明白..为啥dfs错误了..求助

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<iomanip>
using namespace std;
int map[405][405];
bool mark[405][405];
const int dx[8]={-1,1,2,2,1,-1,-2,-2};
const int dy[8]={2,2,1,-1,-2,-2,-1,1};
int n,m;
int x,y;
void dfs(int a,int b,int k)
    {if(a<1||a>n||b<1||b>m) return;
      mark[a][b]=1;
     if(map[a][b]>=k)
	   map[a][b]=k;
     for(int i=0;i<8;i++)
        dfs(a+dx[i],b+dy[i],k+1);
    //if(b+1<=m&&a+2<=n) dfs(a+2,b+1,k+1);
    //if(b-1>0&&a+2<=n) dfs(a+2,b-1,k+1); 
    //if(b+2<=m&&a+1<=n) dfs(a+1,b+2,k+1);
    //if(b+2<=m&&a-1>0) dfs(a-1,b+2,k+1);
    //if(b-1>0&&a-2>0) dfs(a-2,b-1,k+1);
    //if(b+1<=m&&a-2>0) dfs(a-2,b+1,k+1);
    //if(b-2>0&&a+1<=n) dfs(a+1,b-2,k+1);
    //if(b-2>0&&a-1>0) dfs(a-1,b-2,k+1);
	}
int main()
{cin>>n>>m>>x>>y;
for(int i=1;i<=n;i++)
   for(int j=1;j<=m;j++)
       map[i][j]=999999;
dfs(1,1,0);
for(int i=1;i<=n;i++)
   {for(int j=1;j<=m;j++)
       {if(mark[i][j]==0) printf("%-5d",-1);;
        if(mark[i][j]!=0)
		  printf("%-5d",map[i][j]);;
	   }
	cout<<endl;
   } 
return 0;
}