[leetcode 103]Binary Tree Zigzag Level Order Traversal

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本文介绍了如何使用zigzagLevelOrder方法遍历二叉树节点的值，并通过实例展示了实现过程。重点突出了zigzagLevelOrder的特性及应用。

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},

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) {
        vector<vector<int> > res;
        if (root == NULL) {
            return res;
        }
        vector<int> r;
        r.push_back(root->val);
        res.push_back(r);
        int count = 1;
        int order = 0;
        vector<TreeNode *> path;
        path.push_back(root);
        while (!path.empty()) {
            auto t = path.front();
            if (t->left) {
                path.push_back(t->left);
            }
            if (t->right) {
                path.push_back(t->right);
            }
            path.erase(path.begin());
            count --;
            if (count == 0) {
                vector<int> tmp;
                if (!order) {
                    for (vector<TreeNode *>::iterator iter = path.end()-1; iter >= path.begin(); iter--) {
                        tmp.push_back((*iter)->val);
                    }
                } else {
                    for (vector<TreeNode *>::iterator iter = path.begin(); iter != path.end(); iter++) {
                        tmp.push_back((*iter)->val);
                    }
                }
                order = !order;
                if (tmp.size()>0) {
                    res.push_back(tmp);
                }
                count = path.size();
            }
        }
        return res;
    }
};