leetcode 257. Binary tree paths all paths to a binary tree (simple)

One 、 The main idea of the topic

label :  Search for

https://leetcode.cn/problems/binary-tree-paths

Give you the root node of a binary tree  root , Press   In any order  , Return all paths from the root node to the leaf node .

Leaf node   A node without children .

Example  1：

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

Example  2：

Input ：root = [1] Output ：["1"]

Tips ：

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

Two 、 Their thinking

dfs Solve it

3、 ... and 、 How to solve the problem

3.1 Java Realization

/**
 * 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) {
 List<String> ans = new ArrayList<>();
 dfs(root, &quot;&quot;, ans);
 return ans;
 }

 void dfs(TreeNode node, String path, List<String> ans) {
 boolean end = true;
 if (&quot;&quot;.equals(path)) {
 path = String.valueOf(node.val);
 } else {
 path += &quot;->&quot; + node.val;
 }
 if (node.left != null) {
 dfs(node.left, path, ans);
 end = false;
 }
 if (node.right != null) {
 dfs(node.right, path, ans);
 end = false;
 }
 if (end) {
 ans.add(path);
 }
 }
}


Four 、 Summary notes

• 2022/6/11  Finish the first few intermediate search questions , It's easy to do something simple