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] ]
/** * 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) { // Start typing your C/C++ solution below // DO NOT write int main() function vector<vector<int> > ans; if ( !root ) return ans; int flag=0; deque<int> level; vector<TreeNode*> cur; vector<TreeNode*> next; cur.push_back(root); while(!cur.empty()) { level.clear(); next.clear(); int start=0; int end=cur.size(); while(start!=end) { TreeNode* tmp=cur[start]; if ( flag ) level.push_front(tmp->val); else level.push_back(tmp->val); if ( tmp->left ) next.push_back(tmp->left); if ( tmp->right) next.push_back(tmp->right); start++; } ans.push_back(vector<int>(level.begin(),level.end())); cur=next; flag=1-flag; } return ans; } };