codility CountTriangles

Question:codility Lesson15 CountTriangles

My Answer:

def solution(A):    A.sort()    lenA = len(A)    res = 0    for i in range(lenA - 2):        k = i + 2        for j in range(i + 1,lenA - 1):            while k < lenA and A[i] + A[j] > A[k]:                k += 1            res += k - j - 1    return res