SumRootToLeafNo125.java

public class SumRootToLeafNo125 {


    /*
     * You are given the root of a binary tree containing digits from 0 to 9 only.
        Each root-to-leaf path in the tree represents a number.
        For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123.
        Return the total sum of all root-to-leaf numbers. 
        Test cases are generated so that the answer will fit in a 32-bit integer.
        A leaf node is a node with no children.
     */

     // 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 int sumNumbers (TreeNode root) {
            return dfs(root , 0) ;
        }
        private int dfs(TreeNode node , int ans){
            if (node == null) return 0 ;
            ans = ans*10 + node.val ;
            if (node.left == null && node.right == null) return ans; 
            return dfs(node.left, ans) + dfs(node.right, ans); 
        }
      }
}