def compute_lcw(string_1, string_2):
    val = [[-1]*(len(string_2) + 1) for _ in range(len(string_1) + 1)]
    for i in range(len(string_1) + 1):
        val[i][len(string_2)] = 0
    for j in range(len(string_2)):
        val[len(string_1)][j] = 0
    lcw_i = lcw_j = -1
    lcw_len = 0
    for i in range(len(string_1) - 1, -1, -1):
        for j in range(len(string_2)):
            if string_1[i] != string_2[j]:
                val[i][j] = 0
            else:
                val[i][j] = 1 + val[i + 1][j + 1]
                if lcw_len < val[i][j]:
                    lcw_len = val[i][j]
                    lcw_i = i
                    lcw_j = j
    return lcw_len, lcw_i, lcw_j
string_1 = 'bull'
string_2 = 'bullied'
lcw_len, lcw_i, lcw_j = compute_lcw(string_1, string_2)
print("最长公共子串是：")
if lcw_len > 0:
    print(string_1[lcw_i:lcw_i + lcw_len])

最长公共子串是：
bull