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[leetcode] Binary Tree Zigzag Level Order Traversal
Binary Tree Zigzag Level Order Traversal
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},
3 / 9 20 / 15 7
return its zigzag level order traversal as:
[ [3], [20,9], [15,7]]
思路：
BFS的基础题目。
题解：
/** * 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> > res; vector<int> tmp; queue<TreeNode *> q; bool flag = true; int count = 0, num = 1; if(root==NULL) return res; q.push(root); while(!q.empty()) { count = 0; for(int i=0;i<num;i++) { root = q.front(); q.pop(); tmp.push_back(root->val); if(root->left) { q.push(root->left); count++; } if(root->right) { q.push(root->right); count++; } } num = count; if(!flag) reverse(tmp.begin(), tmp.end()); flag = !flag; res.push_back(tmp); tmp.clear(); } return res; }};
[leetcode] Binary Tree Zigzag Level Order Traversal
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