[leetcode]Sum Root to Leaf Numbers

Sum Root to Leaf Numbers

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.

算法思路：

DFS。

代码如下：

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int res = 0;
    public int sumNumbers(TreeNode root){
        if(root == null) return res;
        dfs(root,0);
        return res;
    }
    private void dfs(TreeNode root,int num){
        if(root == null) return;
        if(root.left == null && root.right == null){
            res += 10 * num + root.val;
            return;
        }
        num = num * 10 + root.val;
        if(root.left != null){
            dfs(root.left,num);
        }
        if(root.right != null){
            dfs(root.right,num);
        }
    }
    
}