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.
SOLUTION 1:
使用递归完成。我们要做的是 把左右子树的path加起来。
base case: root是叶子节点时，直接计算path。我们用pre保留上一层计算出来的数字的值。那么到了当前根节点应该就是
把上一层的值*10再加上root的值。
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int sumNumbers(TreeNode root) {
return dfs(root, 0);
} public int dfs(TreeNode root, int pre) {
if (root == null) {
return 0;
} int cur = pre * 10 + root.val;
if (root.left == null && root.right == null) {
return cur;
} return dfs(root.left, cur) + dfs(root.right, cur);
}
}
GITHUB:
https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/tree/SumNumbers_1208_2014.java