[LeetCode] Binary Tree Zigzag Level Order Traversal

最新推荐文章于 2021-02-05 11:10:39 发布

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本文介绍了一种算法，用于实现二叉树节点值的锯齿形层序遍历。从左到右再从右到左交替进行，并提供了一个具体的示例来展示如何实现这一遍历方式。

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).

For example:
Given binary tree {3,9,20,#,#,15,7},

return its zigzag level order traversal as:

[
  [3],
  [20,9],
  [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> > zigzagLevelOrder(TreeNode *root) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        vector<vector<int>> ret;
        stack<TreeNode *> currentLevel;
        stack<TreeNode *> nextLevel;
        if(root == NULL) return ret;
        currentLevel.push_back(root);
        bool leftToRight = true;
        while(currentLevel.size() > 0) {
            nextLevel.clear();
            vector<int> v;
            while(!currentLevel.empty()) {
                v.push()
            }
            if(leftToRight) {
                ret.push_back(v);
                leftToRight = false;
            }else {
                leftToRight = true;
                reverse(v.begin(),v.end());
                ret.push_back(v);
            }
            currentLevel.clear();
            currentLevel.assign(nextLevel.begin(),nextLevel.end());
        }
        return ret;
    }
};