Count no Of triangles

class Solution:
    #Function to count the number of possible triangles.
    def findNumberOfTriangles(self, arr, n):
        arr.sort()
        ans=0
        for i in range(n-1,1,-1):
            l,r=0,i-1
            while l<r:
                if arr[l]+arr[r]>arr[i]:
                    ans=ans+(r-l)
                    r=r-1
                else:
                    l=l+1
        return ans