Leetcode: 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.
主要是看你如何设计这个Recursion 这是一道树的题目,一般使用递归来做,主要就是考虑递归条件和结束条件。想到这样设计Recursion其实还挺难的
1 public class Solution { 2 public int sumNumbers(TreeNode root) { 3 if (root == null) return 0; 4 return helper(root, 0); 5 } 6 7 public int helper(TreeNode root, int sum) { 8 if (root.left==null && root.right==null) return 10*sum+root.val; 9 else if (root.left == null) return helper(root.right, 10*sum+root.val); 10 else if (root.right == null) return helper(root.left, 10*sum+root.val); 11 else { 12 return helper(root.left, 10*sum+root.val) + helper(root.right, 10*sum+root.val); 13 } 14 } 15 }
推荐做法:
1 public int sumNumbers(TreeNode root) { 2 return helper(root,0); 3 } 4 private int helper(TreeNode root, int sum) 5 { 6 if(root == null) 7 return 0; 8 if(root.left==null && root.right==null) 9 return sum*10+root.val; 10 return helper(root.left,sum*10+root.val)+helper(root.right,sum*10+root.val); 11 }