Binary Tree Paths

Leetcode 257.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
/**
 * 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<>();
       if(root == null)
         return ans;
        StringBuilder sb = new StringBuilder();
        backtricking(root,ans,sb);
       return ans;
    }
    public void backtricking(TreeNode root,List<String> ans,StringBuilder input){
      //stop condition 
      if(root == null){       
        return;
      }

      StringBuilder sb = new StringBuilder();
      //pprocess nodes 
      if(input.length() == 0){
        sb.append(root.val);
        input.append(sb.toString());
      }else{
        sb.append("->");
        sb.append(root.val);
        input.append(sb.toString());
      }
      //collect the result 
      if(root.left == null && root.right == null){
        ans.add(input.toString());
      }
      //left and right 
      //recursion 
      backtricking(root.left,ans,input);
      backtricking(root.right,ans,input);
     //undo the previous operation 
      input.delete(input.length() - sb.length(),input.length());
    }
}