题目链接: Binary Tree PostOrder Trveral

题目意思: 给定一棵二叉树，求后续遍历序列

代码:

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void getPostOrder (TreeNode *root, vector& output);
    vector postorderTraversal(TreeNode *root);
};

void Solution::getPostOrder(TreeNode *root, vector& output) {
    if (NULL == root) {
        return;    
    }
    getPostOrder(root->left, output);
    getPostOrder(root->right, output);
    output.push_back(root->val);
}

vector Solution::postorderTraversal(TreeNode *root) {
    vector output;
    output.clear();
    getPostOrder(root, output);
    return output;
}