题解：

class Solution 
{
    int n,m;
    bool st[100][100];
    int flag;
    int dx[8]={-1,-2,-2,-1,1,2,2,1};
    int dy[8]={-2,-1,1,2,2,1,-1,-2};
public:
    bool checkValidGrid(vector<vector<int>>& grid) 
    {
        m = grid.size();
        n = grid[0].size();
        dfs(grid,0,0,0);
        return flag;
    }
    void dfs(vector<vector<int>>& grid,int i,int j,int u)
    {
        st[i][j] = true;
        if(grid[i][j] != u) return;

        if(grid[i][j] == n * m -1)//遍历完所有数组了就可以返回了
        {
            flag = true;
            return;
        }
        for(int k=0;k<8;k++)
        {
            int x=i+dx[k];
            int y=j+dy[k];
            if(x>=0 && x<n && y>=0 && y<m && !st[x][y])
            {
                st[x][y]=true;
                dfs(grid,x,y,u+1);
                st[x][y]=false;
            }

        }
    }

};