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.
Note: A leaf is a node with no children.
Example:
Input: [1,2,3]
1
/ \
2 3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
Example 2:
Input: [4,9,0,5,1]
4
/ \
9 0
/ \
5 1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.
Solution Using DFS:
We will DFS(Depth First Search) to find the numbers and add them to the sum, the time complexity would be O(N).
class HackerHeap {
public int sumNumbers(TreeNode root) {
if (root == null) return 0;
return dfs(root, 0, 0);
}
public int dfs(TreeNode node, int num, int sum) {
if(node == null) return sum;
num = num*10 + node.val;
if(node.left == null && node.right == null) {
return sum+=num;
}
return dfs(node.left, num, sum) + dfs(node.right, num, sum);
}
}
In this video explanation we will solve Leetcode Sum Root to Leaf Numbers Java Solution