BiruLyu
5/29/2017 - 5:39 PM

257. Binary Tree Paths(StringBuilder).java

``````/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<String> binaryTreePaths(TreeNode root) {
List<String> res = new ArrayList<String>();
if(root != null) helper(root, "", res);
return res;
}

public void helper(TreeNode node, String str, List<String> res){
if(node.left == null && node.right == null) res.add(str + node.val);
if(node.left != null) helper(node.left, str + node.val + "->", res);
if(node.right != null) helper(node.right, str + node.val + "->", res);
}
}``````
``````/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<String> binaryTreePaths(TreeNode root) {
List<String> res = new ArrayList<String>();
if (root == null) return res;
StringBuilder sb = new StringBuilder();
sb.append(root.val);
if(root.left == null && root.right == null){//[1] Output : ["1"]
} else {
backtracking(root.left, res, sb);
backtracking(root.right, res, sb);
}

return res;
}

public void backtracking(TreeNode root, List<String> res, StringBuilder temp){
if(root == null) return;

temp.append("->").append(root.val);

if(root.left == null && root.right == null) {