二叉树 --5.1.3 Binary Tree Zigzag Level Order Traversal --图解_数据结构 binary tree zigzag level order traversal-优快云博客

本文介绍了一种解决二叉树之字形层序遍历问题的算法，通过使用队列和标志位实现从左到右再从右到左的交替遍历，最终返回各层节点值的列表。

/**********************************************************************************************************
Given a binary tree, return the zigzag level order traversal of its nodes’ values. (ie, from le to right,
then right to le for the next level and alternate between).
For example: Given binary tree 3,9,20,#,#,15,7,
3
/ \
9 20
/ \
15 7
return its zigzag level order traversal as:
[
[3],
[20,9],
[15,7]
]
**********************************************************************************************************/

Class Solution{
public:
        vector<vector<int> > levelOrder(TreeNode * root){
            vector<vector<int>> reulst;
            if(root == nullptr) return result;
            queue<TreeNode*> q;
            bool left_to_right = true;
            vector<int> level;
            q.push(root);
            q.push(nullptr);//用来分割层
            while(!q.empty()){
                TreeNode * cur = q.front();
                q.pop();
                if(cur){
                    level.push_back(cur->val);
                    if(node->left) q.push(cur->left);
                    if(node->right) q.push(cur->right);
                }else{
                    if(left_to_right){
                        result.push_back(level);
                    }else{
                        reverse(level.begin(),level,end());
                        result.push_back(level);
                    }
                    level.clear();
                    left_to_right = !left_to_right;
                    if(q.size() > 0) q.push(nullptr);
                }    
            }
            return result;
        }
};