[leetcode]103. Binary Tree Zigzag Level Order Traversal

[leetcode]103. Binary Tree Zigzag Level Order Traversal

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Analysis

fighting—— [每天刷题并不难0.0]

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).

Explanation:

Traversing the given binary tree by level, first level:from left to right, second level:from right to left, third level:from left to right…

Implement

/**
 * 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) {
        vector<vector<int>> res;
        if(!root)
            return res;
        
        queue<TreeNode*> nq;
        nq.push(root);
        bool left2right = true;
        while(!nq.empty()){
            int size = nq.size();
            vector<int> tmp;
            for(int i=0; i<size; i++){
                TreeNode* node = nq.front();
                nq.pop();
                tmp.push_back(node->val);
                if(node->left)
                    nq.push(node->left);
                if(node->right)
                    nq.push(node->right);
            }
            if(!left2right)
                reverse(tmp.begin(), tmp.end());
            res.push_back(tmp);
            left2right = !left2right;
        }
        return res;
    }
};