_124.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.TreeNode;

/**
 * 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.
 */
public class _124 {

    int max = Integer.MIN_VALUE;
    public int maxPathSum(TreeNode root) {
        dfs(root);
        return max;
    }

    private int dfs(TreeNode root) {
        if (root == null) {
            return 0;
        }

        int left = Math.max(dfs(root.left), 0);
        int right = Math.max(dfs(root.right), 0);

        max = Math.max(max, root.val + left + right);

        return root.val + Math.max(left, right);
    }

}