[LeetCode]Binary Tree Zigzag Level Order Traversal

最新推荐文章于 2021-02-05 11:10:39 发布

原创最新推荐文章于 2021-02-05 11:10:39 发布 · 135 阅读

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#二叉树

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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例子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]
]

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

请参看http://blog.youkuaiyun.com/honze/article/details/39054413

/**
 * 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) {
        vector<vector<int> > result;
        if (!root) return result;
        vector<int> level;
        queue<TreeNode *> q, next;
        q.push(root);
        bool zag = false;
        while (!q.empty())
        {
            while (!q.empty())
            {
                TreeNode *n = q.front(); q.pop();
                if (n->left) next.push(n->left);
                if (n->right) next.push(n->right);
                level.push_back(n->val);
            }
            if (zag) reverse(level.begin(), level.end());
            result.push_back(level);
            level.clear();
            swap(q, next);
            zag = !zag;
        }
        return result;
    }
};