二叉树 --5.1.3 Binary Tree Zigzag Level Order Traversal --图解

/**********************************************************************************************************
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;}
};

使用队列完成对二叉树的遍历，每层的结束使用nullptr作为分割符

参考资料：

LeetCode题解

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