129. Sum Root to Leaf Numbers - jiejackyzhang/leetcode-note GitHub Wiki
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.
解题思路为DFS，recuisive。
- 若node是null，返回0；
- 若node是lead（左右孩子都是null），返回path number；
- 若node是中间节点，返回左右孩子的返回值之和。
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int sumNumbers(TreeNode root) {
return helper(root, 0);
}
private int helper(TreeNode node, int path) {
if(node == null) return 0;
path = path * 10 + node.val;
if(node.left == null && node.right == null) {
return path;
} else {
return helper(node.left, path) + helper(node.right, path);
}
}
}