Leetcode 687. 最长同值路径

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    int res;
    public int longestUnivaluePath(TreeNode root) {
        dfs(root);
        return res;
    }
    public int dfs(TreeNode root)
    {
        if(root == null)return 0;
        int l=0,r=0;
        if(root.left!=null)
        {
            int lv=root.left.val;
            int tep=dfs(root.left);
            if(lv==root.val)
            {    l=tep+1;
            }
        }
        if(root.right!=null)
        {
            int lv=root.right.val;
            
            int tep=dfs(root.right);
            if(lv==root.val)
            {    r=tep+1;
            }
        }
        res=res>l+r?res:l+r;
        return l>r?l:r;
    }
}