【简单】Lintcode 68:Binary Tree Postorder Traversal

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本文介绍了一种使用递归方法实现二叉树后序遍历的算法，并提供了具体的C++代码示例。该算法首先遍历左子树，然后遍历右子树，最后访问根节点。

Given a binary tree, return the postorder traversal of its nodes' values.

Have you met this question in a real interview?

Yes

Example

Given binary tree {1,#,2,3},

return [3,2,1].

解题思路：

递归。与前序遍历代码几乎相同，仅仅是位置不同。

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: A Tree
     * @return: Postorder in ArrayList which contains node values.
     */
     vector<int> result;
    vector<int> postorderTraversal(TreeNode * root) 
    {
        // write your code here
        if(root == NULL) return result;
        
        if(root->left != NULL)
            result = postorderTraversal(root->left);
            
        if(root->right != NULL)
            result = postorderTraversal(root->right);
        
        result.push_back(root->val);
        
        return result;
    }
};