[leetcode] 102. Binary Tree Level Order Traversal

Binary Tree Level Order Traversal

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,null,null,15,7],

  3
 / \
9 20
    / \
   15 7

return its level order traversal as:

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

我的代碼

簡單的bfs。

/**
 * 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>> rlt;
        queue<TreeNode*> q;
        if (root)
        {
            q.push(root);
            while(q.size()!=0)
            {
                vector<int> qTmp; //一定要注意要先創建一個vector，再往vector<vector<>>裏面放
                int _siz=q.size();
                while(_siz)
                {
                    TreeNode* tmp = q.front();
                    qTmp.push_back(tmp->val);
                    if (tmp->left)
                    {
                        q.push(tmp->left);
                    }
                    if (tmp->right)
                    {
                        q.push(tmp->right);
                    }
                    q.pop();
                    _siz--;
                }
                rlt.push_back(qTmp);
            }

        }
        return rlt;
    }
};