給出一棵二叉樹(shù)，尋找一條路徑使其路徑和最大，路徑可以在任一節(jié)點(diǎn)中開(kāi)始和結(jié)束（路徑和為兩個(gè)節(jié)點(diǎn)之間所在路徑上的節(jié)點(diǎn)權(quán)值之和）

樣例
給出一棵二叉樹(shù)：

   1
  / \
 2   3

返回 6

代碼:

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: An integer.
     */
   int max = Integer.MIN_VALUE;
    public int maxPathSum(TreeNode root) {
        if(null == root)
        {
            return 0;
        }
        subMaxPathSum(root);
        return max;
        }
    
    public int subMaxPathSum(TreeNode node)
    {
        if(null == node)
        {
            return 0;
        }
        int leftMax = subMaxPathSum(node.left);
        int rightMax = subMaxPathSum(node.right);
        int subMax = Math.max(Math.max(Math.max(leftMax + node.val, rightMax + node.val), node.val),leftMax + rightMax + node.val);
        if(max < subMax)
        {
            max = subMax;
        }
        return Math.max(Math.max(leftMax + node.val, rightMax + node.val), node.val);
    }
}