[leetcode]Binary Tree Paths

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public class Solution { List<String> result = new ArrayList<String>(); public List<String> binaryTreePaths(TreeNode root) { rec(root, ""); return result; } private void rec(TreeNode root, String str){ if (root == null) return; if (root.left == null && root.right == null){ result.add(str+root.val); } rec(root.left, str+root.val+"->"); rec(root.right, str+root.val+"->"); } }