Leetcode:sum Root to Leaf Numbers problem solving report

Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 to, 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.

Solution 1:

Use recursion to complete. All we have to do is add the path of the left and right subtree.

When base case:root is a leaf node, the path is calculated directly. We use the pre to retain the value of the calculated number from the previous layer. So the current root node should be

*10 the value of the previous layer to the root value.

1 /**2 * Definition for binary tree3 * public class TreeNode {4 * int val;5 * TreeNode left;6 * TreeNode right;7 * TreeNode (int x) {val = x;}8  * }9  */Ten  Public classSolution { One      Public intsumnumbers (TreeNode root) { A         returnDFS (root, 0); -     } -      the      Public intDFS (TreeNode root,intpre) { -         if(Root = =NULL) { -             return0; -         } +          -         intCur = Pre * 10 +Root.val; +         if(Root.left = =NULL&& Root.right = =NULL) { A             returncur; at         } -          -         returnDFS (root.left, cur) +dfs (root.right, cur); -     } -}

View Code

GITHUB:

Https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/tree/SumNumbers_1208_2014.java

Leetcode:sum Root to Leaf Numbers problem solving report