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;}}}};