binary-tree-level-order-traversal

//层次遍历二叉树

题目描述

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]
]

/**
 * Definition for binary tree
 * 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)    return result;
        
        TreeNode *p = root;
        
           queue<TreeNode*> q;
        q.push(root);
        int count = 1;
        int level = 0;
        
        vector<int> tmp;
        while(!q.empty()){
            tmp.clear();
            level = 0;
            for(int i = 0;i < count; ++i){
                root = q.front();
                q.pop();
                tmp.push_back(root->val);
                
                if(root->left != NULL){
                    q.push(root->left);
                    ++level;
                }
                
                if(root->right != NULL){
                    q.push(root->right);
                    ++level;
                }
            }
            count = level;
            result.push_back(tmp);
        }
        return result;
    }
};