79.最长公共子串

def longestCommonSubstring(self, A, B):  
    # write your code here  
    if A == ‘‘ or B == ‘‘:  
        return 0  
    if len(A) >= len(B):  
        L, L1 = A[:], B[:]  
    else:  
        L, L1 = B[:], A[:]  
    L = [L[i:j] for i in range(len(L)) for j in range(1, len(L)+1) if i < j]  
    return max([len(i) for i in L if i in L1])