leetcode124

 class Solution {
     int maxValue;
     public int maxPathSum(TreeNode root) {
         maxValue = Integer.MIN_VALUE;
         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;
     }
 }

参考：https://leetcode.com/problems/binary-tree-maximum-path-sum/discuss/39775/Accepted-short-solution-in-Java