Question
Given a non-empty binary tree, find the maximum path sum.
For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain at least one node and does not need to go through the root.
Example 1:
Input: [1,2,3]
1
/ \
2 3
Output: 6
Example 2:
Input: [-10,9,20,null,null,15,7]
-10
/ \
9 20
/ \
15 7
Output: 42
Solution
TODO
Code
Here is a sample solution.
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
int maxSum = Integer.MIN_VALUE;
public int maxPathSum(TreeNode root) {
maxPathSumFrom(root);
return maxSum;
}
public int maxPathSumFrom(TreeNode root) {
if(root == null) return Integer.MIN_VALUE;
int left = maxPathSumFrom(root.left);
int right = maxPathSumFrom(root.right);
int sum = root.val;
if(left > 0) sum += left;
if(right > 0) sum += right;
maxSum = Math.max(sum, maxSum);
if(left < 0 && right < 0) return root.val;
return Math.max(left, right) + root.val;
}
}
Performance
O(n)