124. Binary Tree Maximum Path Sum
A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.
The path sum of a path is the sum of the node's values in the path.
Given the root of a binary tree, return the maximum path sum of any non-empty path.
Example 1:
Input: root = [1,2,3]
Output: 6
Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.
Example 2:
Input: root = [-10,9,20,null,null,15,7]
Output: 42
Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.
Constraints:
- The number of nodes in the tree is in the range [1, 3 * 104].
- -1000 <= Node.val <= 1000
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
private int maxValue = Integer.MIN_VALUE;;
public int maxPathSum(TreeNode root){
maxPathDown(root);
return maxValue;
}
private int maxPathDown(TreeNode node) {
if(node == null){
return 0;
}
int left = Math.max(0, maxPathDown(node.left));
int right = Math.max(0, maxPathDown(node.right));
maxValue = Math.max(maxValue, left + right + node.val);
return Math.max(left, right) + node.val;
}
}