Longest Increasing Path in a Matrix

class Solution {
public:
    int longestIncreasingPath(vector<vector<int>>& matrix) {
        int m=matrix.size();
        if(m == 0) return 0;
        int n=matrix[0].size();
        if(n == 0 ) return 0;
        vector<int> row(n,0);
        vector<vector<int>> len(m,row);
        //cout<<m<<endl;
        //cout<<n<<endl;
        int max_len = 0;
        for(int i=0;i<m;i++)
         for(int j=0;j<n;j++)
         { //cout<<i<<" "<<j<<endl;
           max_len=max(max_len,getlen(matrix,len,i,j));
         } 
         return max_len;
        
    }
    int getlen(vector<vector<int>>& matrix,vector<vector<int>>& len,int i,int j){
          int m=matrix.size();
          int n=matrix[0].size();
          //cout<<"i="<<i<<" j="<<j<<endl;
          if(i<0 || i> m-1 || j<0 || j>n-1) {return 0;}
          if(len[i][j] != 0) {cout<<len[i][j]<<endl; return len[i][j];}
          int a,b,c,d;
          a=b=c=d=1;
          
        if(i==0) a=1;
        else {
            if(matrix[i][j]<matrix[i-1][j]) 
            a=getlen(matrix,len,i-1,j)+1;
        }
        //   cout<<"a="<<a<<endl;
        if(i==m-1) b=1;
        else {
            if(matrix[i][j]<matrix[i+1][j]) 
            b=getlen(matrix,len,i+1,j)+1;
        }
        //   cout<<"b="<<b<<endl;
        if(j==0) c=1;
        else {
            if(matrix[i][j]<matrix[i][j-1]) 
                 c=getlen(matrix,len,i,j-1)+1;
        }
         //  cout<<"c="<<c<<endl;
        if(j==n-1) d=1;
        else {
            if(matrix[i][j]<matrix[i][j+1])
            d=getlen(matrix,len,i,j+1)+1;
        }
         //  cout<<"d="<<d<<endl;
        
        len[i][j] = max(a,max(b,max(c,d)));
        return len[i][j];
    }
};

a.b.c.d分别表示上下左右；

备忘录的思想；

数字的大小关系决定了不可能循环！！这是潜在条件