Binary Tree Postorder Traversal

最新推荐文章于 2022-07-19 11:52:33 发布

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本文详细介绍了如何通过迭代方法实现二叉树的后序遍历，提供了与递归方法对比的算法实现，并解释了迭代方法在效率和内存使用上的优势。

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

For example:
Given binary tree {1,#,2,3},

return [3,2,1].

Note: Recursive solution is trivial, could you do it iteratively?

/**
 * 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<int> postorderTraversal(TreeNode *root)
	{
		vector<int> res;
		stack<TreeNode* > sta;

		TreeNode* cur = root;
		TreeNode* pre = 0;
		while (0 != cur || !sta.empty())
		{
			if (0 != cur)
			{
				sta.push(cur);
				cur = cur->left;
			}
			else if (!sta.empty())
			{
				TreeNode* tmp = sta.top();
				if (0 == tmp->right || tmp->right == pre)
				{
					res.push_back(tmp->val);
					sta.pop();
					pre = tmp;
				}
				else 
					cur = tmp->right;
			}
		} 
		return res;
    }
};