655. Print Binary Tree

Print a binary tree in an m*n 2D string array following these rules:

The row number m should be equal to the height of the given binary
tree. The column number n should always be an odd number. The root
node’s value (in string format) should be put in the exactly middle of
the first row it can be put. The column and the row where the root
node belongs will separate the rest space into two parts (left-bottom
part and right-bottom part). You should print the left subtree in the
left-bottom part and print the right subtree in the right-bottom part.
The left-bottom part and the right-bottom part should have the same
size. Even if one subtree is none while the other is not, you don’t
need to print anything for the none subtree but still need to leave
the space as large as that for the other subtree. However, if two
subtrees are none, then you don’t need to leave space for both of
them. Each unused space should contain an empty string “”. Print the
subtrees following the same rules. Example 1:

/*> 引用块内容* * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<vector<string>> printTree(TreeNode* r) {        int d = hight(r);        vector<vector<string>> res(d,vector<string>(pow(2,d)-1,""));        DFS(r,0,res,0,res[0].size()-1);        return res;    }    int hight(TreeNode* r){        if(!r)return 0;        return max(hight(r->left),hight(r->right))+1;    }    void DFS(TreeNode* root,int d,vector<vector<string>>& res, int L, int r ){        int mid = (L+r)/2;        res[d][mid] = to_string(root->val);        if(root->left)DFS(root->left,d+1,res,L,mid-1);        if(root->right)DFS(root->right,d+1,res,mid+1,r);    }};