LeetCode 124.二叉树的最大路径和

​​https://leetcode-cn.com/problems/binary-tree-maximum-path-sum/​​

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int max = Integer.MIN_VALUE;
    public int maxPathSum(TreeNode root) {
        
        findMaxPath(root);
        return max;
    }
      public int findMaxPath(TreeNode root) {
          if(root==null){
          //结点为空，那么最大权值是0
              return 0;
          }
            //求左右子树的最大权值，与0比较是为了舍弃负值
            int lMax = Math.max(findMaxPath(root.left),0);
            int rMax = Math.max(findMaxPath(root.right),0);
            //比较包括根结点的最大路径值
            max = Math.max(max,lMax+rMax+root.val);

            return root.val+Math.max(lMax,rMax);
    }
}