[leetcode刷题系列]Binary Tree Zigzag Level Order Traversal

和前面的某道题类似- -

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    vector<vector<int>> ret;
    void dfs(TreeNode * root, int dep){
        if(ret.size() < dep)
            ret.resize(dep);
        ret[dep - 1].push_back(root->val);
        if(root->left != 0)
            dfs(root->left, dep + 1);
        if(root->right != 0)
            dfs(root->right, dep + 1);
    }
public:
    vector<vector<int> > zigzagLevelOrder(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ret.clear();
        if(root == 0)
            return ret;
        dfs(root, 1);
        for(int i = 1; i < ret.size(); i += 2)
            reverse(ret[i].begin(), ret[i].end());
        return ret;
    }
};