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.     1
  2.    / \
  3.   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

  1. // Sum root to leaf numbers
  2. // 时间复杂度O(n)，空间复杂度O(logn)
  3. public class Solution {
  4.     public int sumNumbers(TreeNode root) {
  5.         return dfs(root, 0);
  6.     }
  7.     private static int dfs(TreeNode root, int sum) {
  8.         if (root == null) return 0;
  9.         if (root.left == null && root.right == null)
  10.             return sum * 10 + root.val;
  12.         return dfs(root.left, sum * 10 + root.val) +
  13.                 dfs(root.right, sum * 10 + root.val);
  14.     }
  15. }

原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/java/binary-tree/recursion/sum-root-to-leaf-numbers.html