427. 建立四叉树

class Solution {
public:Node* construct(vector<vector<int>>& grid) {int n = grid.size();return dfs(grid,0,0,n);}bool allSame(vector<vector<int>>& grid, int x,int y,int len){int val = grid[x][y];for(int i=0;i<len;++i){for(int j=0;j<len;++j){   if(grid[x+i][y+j] != val ){return false;}}}return true;}Node* dfs(vector<vector<int>>& grid,int x,int y,int len){int n = len;// 全部相同if(allSame(grid,x,y,n)){return new Node(grid[x][y]==1,true,nullptr,nullptr,nullptr,nullptr);}// 可以划分成四叉树int binSize = n /2;Node* leftTop     = dfs(grid,x,y,binSize);Node* rightTop    = dfs(grid,x,y+binSize,binSize);Node* leftBottom  = dfs(grid,x+binSize,y,binSize);Node* rightBottom = dfs(grid,x+binSize,y+binSize,binSize);return new Node(false,false,leftTop,rightTop,leftBottom,rightBottom );}
};