【力扣】102.二叉树的层序遍历

AC截图

题目

思路

维持一个队列，每次容纳一层的元素即可。

代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> res;
        if(root==NULL){
            return res;
        }

        deque<TreeNode*> dq;
        dq.push_back(root);
        vector<int> tmp;

        while(!dq.empty()){
            int cnt = dq.size();
            tmp.clear();
            while(cnt>0){
                TreeNode* node = dq.front();
                tmp.push_back(node->val);
                dq.pop_front();
                if(node->left!=NULL){
                    dq.push_back(node->left);
                }
                if(node->right!=NULL){
                    dq.push_back(node->right);
                }
                cnt--;
            }
            res.push_back(tmp);
        } 
        return res;
    }
};