leetcode之Binary Tree Level Order Traverse

方法同上一篇博客的方法类似

C++实现：

/**
 * 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<int>> v;
    void build(TreeNode* root, int depth){
        if(root == NULL)
            return;
        while(v.size()<=depth){
            v.push_back(vector<int>());
        }
        v[depth].push_back(root->val);
        build(root->left, depth+1);
        build(root->right, depth+1);
    }
    vector<vector<int>> levelOrder(TreeNode* root) {
        build(root, 0);
        return v;
    }
};