Sum Root to Leaf Numbers

描述

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.

分析

无

代码

// Sum root to leaf numbers
// 时间复杂度O(n)，空间复杂度O(logn)
public class Solution {
    public int sumNumbers(TreeNode root) {
        return dfs(root, 0);
    }
    private static int dfs(TreeNode root, int sum) {
        if (root == null) return 0;
        if (root.left == null && root.right == null)
            return sum * 10 + root.val;

        return dfs(root.left, sum * 10 + root.val) +
                dfs(root.right, sum * 10 + root.val);
    }
}