Binary Tree Postorder Traversal - Leetcode

最新推荐文章于 2022-07-19 11:52:33 发布

AngelQian2

最新推荐文章于 2022-07-19 11:52:33 发布

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分类专栏： Leetcode

本文链接：https://blog.youkuaiyun.com/Q_wing/article/details/43924921

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本文介绍了一种使用迭代而非递归的方法来实现二叉树的后序遍历算法。通过栈结构辅助，该算法可以高效地遍历二叉树并返回节点值的后序遍历序列。

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/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Integer> postorderTraversal(TreeNode root) {
		Stack<TreeNode> s = new Stack<>();
		List<Integer> result = new ArrayList<>();
		TreeNode pointer = root, prev = null;

		do {
			while (pointer != null) {
				s.push(pointer);
				pointer = pointer.left;
			}
			prev = null;
			while (!s.empty()) {
				pointer = s.pop();
				if (pointer.right == prev) {
					result.add(pointer.val);
					prev = pointer;
				} else {
					s.push(pointer);
					pointer = pointer.right;
					break;
				}
			}
		} while (!s.empty());

		return result;
	}
}

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

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