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  • 19.3.4 [LeetCode 102] 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,null,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 };
    View Code
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  • 原文地址:https://www.cnblogs.com/yalphait/p/10473864.html
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