[leetcode] Binary Tree Postorder Traversal

Iterative way.. 想了一会都没想出来... 网上搜到的都是很复杂的东西..
其实可以通过 root->right->left的traversal 来做...最后把结果倒转一下就好了

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public class Solution { public List<Integer> postorderTraversal(TreeNode root) { ArrayList<Integer> result = new ArrayList<Integer>(); if (root == null){ return result; } Stack<TreeNode> stack = new Stack<TreeNode>(); stack.push(root); while (!stack.isEmpty()){ TreeNode temp = stack.pop(); result.add(temp.val); if (temp.left != null){ stack.push(temp.left); } if (temp.right != null){ stack.push(temp.right); } } Collections.reverse(result); return result; } }