Sum Root to Leaf Numbers

Sum Root to Leaf Numbers

 Total Accepted: 5954 Total
Submissions: 21112My Submissions

Given a binary tree containing digits from 

0-9

 only,
each root-to-leaf path could represent a number.
An example is the root-to-leaf path 

1->2->3

 which
represents the number 

123

.
Find the total sum of all root-to-leaf numbers.
For example,

1
/ \
2   3

The root-to-leaf path 

1->2

 represents
the number 

12

.

The root-to-leaf path 

1->3

 represents the number 

13

.
Return the sum = 12 + 13 = 

25

.

Discuss

DFS

/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int sumNumbers(TreeNode root) {
if (root == null) return 0;
return sumNumbersHelper(root, 0);
}

private int sumNumbersHelper(TreeNode root, int num) {
if (root.left == null && root.right == null)
return num * 10 + root.val;
return (root.left != null ? sumNumbersHelper(root.left, num * 10 + root.val) : 0) + (root.right != null ? sumNumbersHelper(root.right, num * 10 + root.val) : 0);
}
}

或者：

public static int sumNumbers(TreeNode<Integer> root){
if(root == null)
return 0;
return helper(root,0);
}

private static int helper(TreeNode<Integer> root, int n){
if(root==null)
return 0;
n = n * 10 + root.val;
return Math.max(n,helper(root.left,n)+helper(root.right,n));
}