第78题 Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3   / \  9  20    /  \   15   7

return its level order traversal as:

[  [3],  [9,20],  [15,7]]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

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 Tree Breadth-first Search

Solution in C++:

/** * 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>> levelOrder(TreeNode* root) {        vector<vector<int>> result;        if(root==NULL) return result;        queue<TreeNode*> q;        q.push(root);        int numChildren = 1;        while(!q.empty()){            int index = numChildren;            numChildren =0;            vector<int> curLevel;            while(index>0){                TreeNode* cur = q.front();                q.pop();                if(cur->left!=NULL){                    q.push(cur->left);                    numChildren++;                }                if(cur->right!=NULL){                    q.push(cur->right);                    numChildren++;                }                index--;                curLevel.push_back(cur->val);            }            result.push_back(curLevel);        }        return result;    }};