257. Binary Tree Paths

难度: Easy

题目描述

Given the root of a binary tree, return all root-to-leaf paths in any order.

A leaf is a node with no children.

 

Example 1:

Input: root = [1,2,3,null,5]
Output: ["1->2->5","1->3"]

Example 2:

Input: root = [1]
Output: ["1"]

 

Constraints:

• The number of nodes in the tree is in the range [1, 100].
• -100 <= Node.val <= 100

解题思路

代码实现

解决方案

java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode() {}
 * TreeNode(int val) { this.val = val; }
 * TreeNode(int val, TreeNode left, TreeNode right) {
 * this.val = val;
 * this.left = left;
 * this.right = right;
 * }
 * }
 */
class Solution {

    public List<String> binaryTreePaths(TreeNode root) {

        if (root == null) {
            return new ArrayList<>();
        }
        List<String> res = new ArrayList<>();

         binaryTreePaths2(root,"",res);

        return res;

    }

    public void binaryTreePaths2(TreeNode root, String str, List<String> res) {
        if(root==null){
            return;
        }
        String newStr = str+root.val;
            
        if (root.left == null && root.right == null) {
            res.add(newStr);
            return;
        }
        if (root.left != null) {
            binaryTreePaths2(root.left, newStr + "->" , res);
        }
        if (root.right != null) {
            binaryTreePaths2(root.right, newStr + "->", res);
        }

    }

}