给定一个二叉树的头节点head，路径的规定有以下三种不同的规定：
    1）路径必须是头节点出发，到叶节点为止，返回最大路径和
    2）路径可以从任何节点出发，但必须往下走到达任何节点，返回最大路径和

    1.  class TreeNode {
    2.     int val;
    3.     TreeNode left;
    4.     TreeNode right;
    6.     TreeNode(int x) {
    7.         val = x;
    8.     }
    9.  }
    11. public int findmax(TreeNode root)
    12.   {
    13.       if (root==null)
    14.         {
    15.             return 0;
    16.         }
    17.         return f(root).allTreeMaxsum;
    18.     }
    20.   }
    23.     public class Info{
    24.         public int allTreeMaxsum;
    25.         public int fromHeadMaxsum;
    26.         public Info(int all,int from)
    27.         {
    28.             allTreeMaxsum= all;
    29.             fromHeadMaxsum = from;
    30.         }
    31.     }
    32.     public Info f(TreeNode x)
    33.     {
    34.         if (x==null)
    35.         {
    36.             return null;
    37.         }
    38.         Info leftInfo = f(x.left);
    39.         Info rightInfo  =f(x.right);
    40.         int p1=Integer.MIN_VALUE;
    41.         if (leftInfo!=null)
    42.         {
    43.             p1= leftInfo.allTreeMaxsum;
    44.         }
    45.         int p2=Integer.MIN_VALUE;
    46.         if (rightInfo!=null)
    47.         {
    48.             p2 = rightInfo.allTreeMaxsum;
    49.         }
    50.         int p3 = x.val;
    51.         int p4 = Integer.MIN_VALUE;
    52.         if (leftInfo!=null)
    53.         {
    54.             p4 = x.val+leftInfo.fromHeadMaxsum;
    55.         }
    56.         int p5 = Integer.MIN_VALUE;
    57.         if (rightInfo!=null)
    58.         {
    59.             p5 = x.val+rightInfo.fromHeadMaxsum;
    60.         }
    61.         int allTreeMaxsum = Math.max(Math.max(Math.max(p1,p2),p3),Math.max(p4,p5));
    62.         int fromHeadMaxsum = Math.max(p3,Math.max(p4,p5));
    63.         return new Info(allTreeMaxsum,fromHeadMaxsum);
    64.     }