LeetCode 103: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]
]

此题所谓的Zig-Zag 遍历，及第一行从左到有，第二行从右到左，第三行从左到右，依次类推。此题仍然可以在层次遍历后，对结果进行处理。代码如下：

class Solution
{
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root)
    {
        //同层次遍历
        vector<vector<int>>result;
        if (!root)
            return result;
        queue<TreeNode*> vec;
        vec.push(root);
        while (vec.size() > 0) {
            queue<TreeNode*> tmp_vec;
            vector<int> tmp_result;
            while (vec.size() > 0) {
                TreeNode* node = vec.front();
                vec.pop();
                if (node->left)
                    tmp_vec.push(node->left);
                if (node->right)
                    tmp_vec.push(node->right);
                tmp_result.push_back(node->val);
            }

            vec = tmp_vec;
            result.push_back(tmp_result);
        }

        //对第2层、4层。。。进行翻转
        for (int i = 1; i < result.size(); i += 2) {
            reverse(result[i].begin(), result[i].end());
        }
        return result;

    }
};

LeetCode 103:Binary Tree Zigzag Level Order Traversal

原文：http://blog.csdn.net/sunao2002002/article/details/46281175