Leetcode 102. Binary Tree Level Order Traversal

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https://leetcode.com/problems/binary-tree-level-order-traversal/

题意：二叉树的层序遍历

代码：

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/**
 * 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) {
        queue<TreeNode*> q;
        q.push(root);
        vector<vector<int>> res;
        int num = 1;
        while(!q.empty()){
            vector<int> arr;
            int count = 0;
            for(int i = 0; i < num; i++){
                TreeNode* temp = q.front();
                q.pop();
                if(temp){
                    arr.push_back(temp->val);
                    q.push(temp->left);
                    q.push(temp->right);
                    count += 2;
                }
            }
            if(!arr.empty())
                res.push_back(arr);
            num = count;
        }
        
        return res;
    }
};
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