LeetCode 145. Binary Tree Postorder Traversal

考点	难度
Tree	Easy

题目

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

思路

和preorder类似，除了把node加到ans的时候需要倒序。

答案

public List<Integer> postorderTraversal(TreeNode root) {
        LinkedList<Integer> ans = new LinkedList<>();
        Stack<TreeNode> stack = new Stack<>();
        if (root == null) return ans;

        stack.push(root);
        while (!stack.isEmpty()) {
            TreeNode cur = stack.pop();
            ans.addFirst(cur.val);
            if (cur.left != null) {
                stack.push(cur.left);
            }
            if (cur.right != null) {
                stack.push(cur.right);
            } 
        }
        return ans;
}