Max_Path_Sum_Binary_Tree

/**
 * 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 {
    int maxSum = -1001;
    public int maxPathSum(TreeNode root) {
        dfs(root);

        return maxSum;
    }

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

        int left = dfs(root.left);
        int right = dfs(root.right);

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

        return Math.max(Math.max(left,right), 0) + root.val;
    }
}