[刷题]Binary Tree Postorder Traversal

最新推荐文章于 2022-07-19 11:52:33 发布

原创最新推荐文章于 2022-07-19 11:52:33 发布 · 341 阅读

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本文介绍了一种实现二叉树后序遍历的方法，使用递归算法将左右子树的遍历结果合并，并最终返回包含所有节点值的列表。

[LintCode]Binary Tree Postorder Traversal

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Postorder in ArrayList which contains node values.
     */
    public ArrayList<Integer> postorderTraversal(TreeNode root) {
        // 2015-3-22
        ArrayList<Integer> rst = new ArrayList<>();
        if (root == null) {
            return rst;
        }
        
        // divide
        ArrayList<Integer> left = postorderTraversal(root.left);
        ArrayList<Integer> right = postorderTraversal(root.right);
        
        // conquer
        rst.addAll(left);
        rst.addAll(right);
        rst.add(root.val);
        
        return rst;
    }
}