LeetCode系列102—二叉树的层序遍历

题意

102. 二叉树的层序遍历

题解

方法一：广度优先搜索

/**
 * 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>> ans;
        if (!root) return ans;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
    
    
            ans.push_back(vector<int>());
            int n = q.size();
            for (int i = 0; i < n; i++) {
    
    
                TreeNode* head = q.front();
                ans.back().push_back(head->val);
                q.pop();
                if (head->left) q.push(head->left);
                if (head->right) q.push(head->right);
            }
        }
        return ans;
    }
};