Day10: [LeetCode中等] 103. 二叉树的锯齿形层次遍历
题源:
来自leetcode题库:
https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/
思路:
二叉树层次遍历的变种题型,龙摆尾式的层序遍历,做法应该有很多种,我用的是两个栈来回倒腾的方法,倒腾一次说明遍历了一层。具体看代码吧。其实只要熟悉了基本的层序遍历,这题稍加思考就可解决。
代码:
dirty code凑合看吧
/**
* Definition for a binary tree node.
* 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) {
bool zhengxu=true;
stack<TreeNode*> S1,S2;
vector<vector<int> > res;
if(root==NULL) return res;
TreeNode *flag=NULL;
S1.push(root);
while(!(S1.empty()&&S2.empty())){ //两个栈都空了表示遍历完事了
vector<int> temp;
TreeNode *p=NULL;
if(zhengxu){
zhengxu=false;
while(!S1.empty()){
p=S1.top();
S1.pop();
temp.push_back(p->val);
if(p->left!=NULL) S2.push(p->left);
if(p->right!=NULL) S2.push(p->right);
}
}else{
zhengxu=true;
while(!S2.empty()){
p=S2.top();
S2.pop();
temp.push_back(p->val);
if(p->right!=NULL) S1.push(p->right);
if(p->left!=NULL) S1.push(p->left);
}
}
res.push_back(temp);
}
return res;
}
};