Given a binary tree, return all root-to-leaf paths.

Note: A leaf is a node with no children.

Example:

Input:

   1
/ \
2 3
\
5 Output: ["1->2->5", "1->3"] Explanation: All root-to-leaf paths are: 1->2->5, 1->3
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<String> binaryTreePaths(TreeNode root) {
List<String> res = new ArrayList<>();
if (root == null) {
return res;
}
helper(root, res, "");
return res;
} private void helper(TreeNode root, List<String> res, String str) {
if (root == null) {
return;
}
if (root.left == null && root.right == null) {
res.add(str + root.val);
return;
}
String newStr = str + root.val + "->";
helper(root.left, res, newStr);
helper(root.right, res, newStr);
}
}

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