Diameter of the tree

def dia(root,ans):
    if root==None:
        return 0
    l=dia(root.left,ans)
    r=dia(root.right,ans)
    ans[0]=max(ans[0],l+r+1)
    return max(l,r)+1
class Solution:
    def diameterOfBinaryTree(self, root: Optional[TreeNode]) -> int:
        ans=[-1]
        dia(root,ans)
        return ans[0]-1. #No. of nodes in terms of edges, not nodes so reduced 1