【LeetCode】Binary Tree Level Order Traversal（层序遍历）

Question

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]]Solution/** * 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>> out_vec;vector<int> vec;if(root == NULL)return out_vec;queue<TreeNode*> que;que.push(root);int level = 0;int num = 1;while(!que.empty()){vec.clear();level = 0;for(int i = 0; i < num; i ++){root = que.front();que.pop();vec.push_back(root->val);if(root->left != NULL){que.push(root->left);level ++;}if(root->right != NULL){que.push(root->right);level ++;}}num = level;out_vec.push_back(vec);}return out_vec;}};

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