非递归法
/*** 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) {queue<TreeNode*> que;vector<vector<int>> result;if(root) que.push(root);while(!que.empty()) {int size = que.size();vector<int> vec;while(size--) {TreeNode* node = que.front();que.pop();vec.push_back(node->val);if(node->left) que.push(node->left);if(node->right) que.push(node->right);}result.push_back(vec);}return result;}
};
递归法
/*** 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:void order(TreeNode* node, vector<vector<int>>& result, int depth) {if(node == nullptr) return;if(result.size() == depth) result.push_back(vector<int>()); // 如果result没有该层，则插入新层result[depth].push_back(node->val);order(node->left, result, depth + 1);order(node->right, result, depth + 1);}vector<vector<int>> levelOrder(TreeNode* root) {vector<vector<int>> result;order(root, result, 0);return result;}
};
)
