[leetcode 102]Binary Tree Level Order Traversal

最新推荐文章于 2025-12-28 22:03:12 发布

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本文详细介绍了如何实现二叉树的层次遍历，包括使用队列进行节点的逐层遍历，并提供了实例代码来展示整个过程。

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},

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

/**
 * Definition for binary tree
 * 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> > res;
        if (root == NULL) {
            return res;
        }
        vector<TreeNode *> path;
        path.push_back(root);
        int count = 1;
        vector<int> cur;
        cur.clear();
        while (!path.empty()) {
            auto tmp = path.front();
            path.erase(path.begin());
            count--;
            cur.push_back(tmp->val);
            if (tmp->left) {
                path.push_back(tmp->left);
            }
            if (tmp->right) {
                path.push_back(tmp->right);
            }
            if (count == 0) {
                count = path.size();
                res.push_back(cur);
                cur.clear();
            }
        }
        return res;
    }
};