binaryTreeMaximumPathSum.java

// Given a 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.

// For example:
// Given the below binary tree,

//        1
//       / \
//      2   3
// Return 6.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    
    int max = Integer.MIN_VALUE;
    
    public int maxPathSum(TreeNode root) {
        
        maxPathSumRecursive(root);
        return max;
        
    }
    
    private int maxPathSumRecursive(TreeNode root) {
        
        if(root == null) return 0;
        
        int left = Math.max(maxPathSumRecursive(root.left), 0);
        int right = Math.max(maxPathSumRecursive(root.right), 0);
        
        max = Math.max(max, root.val + left + right);
        
        return root.val + Math.max(left, right);
        
        
    }
    
}