19.3.4 [LeetCode 102] Binary Tree Level Order Traversal

发布时间：2020-12-14 04:38:36 所属栏目：大数据来源：网络整理

导读：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,15,7] , 3 / 9 20 / 15 7 ? return its level order traversal as: [ [3],[9,20],

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,15,7],

    3
   /   9  20
    /     15   7

return its level order traversal as:

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

 1 class Solution {
 2 public:
 3     vector<vector<int>> levelOrder(TreeNode* root) {
 4         queue<TreeNode*>q,p;
 5         vector<vector<int>>ans;
 6         if(!root)return ans;
 7         int i = 0;
 8         q.push(root);
 9         while (!q.empty()) {
10             ans.push_back(vector<int>());
11             while (!q.empty()) {
12                 TreeNode*now = q.front(); q.pop();
13                 ans[i].push_back(now->val);
14                 if (now->left)
15                     p.push(now->left);
16                 if (now->right)
17                     p.push(now->right);
18             }
19             q = p;
20             p = queue<TreeNode*>();
21             i++;
22         }
23         return ans;
24     }
25 };

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（编辑：李大同）

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