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二叉树的锯齿形层序遍历⚓︎

Leetcode题目链接

描述⚓︎

详见中文题目链接。

解答⚓︎

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/**
 * 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>> zigzagLevelOrder(TreeNode* root) {
        vector<vector<int>> res;
        if (!root) return res;

        queue<TreeNode*> q;
        q.push(root);
        bool isOrderLeft = true;

        while (!q.empty()) {
            int len = q.size();
            deque<int> level;

            while (len--) {
                TreeNode* node = q.front();
                q.pop();

                if (isOrderLeft) level.push_back(node->val);
                else level.push_front(node->val);

                if (node->left) q.push(node->left);
                if (node->right) q.push(node->right);
            }
            res.emplace_back(vector<int>(level.begin(), level.end()));
            isOrderLeft = !isOrderLeft;
        }
        return res;
    }
};