题目描述Description

For a string \(s_1, s_2, \dots, s_n\), Bobo denotes the number of its distinct substrings as \(f(s_1, s_2, \dots, s_n)\). He also defines \(h(c) = f(s_1, s_2, \dots, s_n, c) - f(s_1, s_2, \dots, s_n)\) for character \(c\).

Given a string \(s_1, s_2, \dots, s_n\) and \(m\), find the value of \(\bigoplus_{c = 1}^{m}\left(h(c) \cdot 3^c \bmod (10^9+7)\right)\).

Note that \(\oplus\) denotes the bitwise exclusive-or (XOR).

输入格式Input

The input consists of several test cases and is terminated by end-of-file.

The first line of each test case contains two integers \(n\) and \(m\).

The second line contains \(n\) integers \(s_1, s_2, \dots, s_n\).

• \(1 \leq n, m \leq 10^6\)
• \(1 \leq s_i \leq m\)
• The sum of \(n\) does not exceed \(5 \times 10^6\).
• The sum of \(m\) does not exceed \(5 \times 10^6\).

输出格式Output

For each test case, print an integer which denotes the result.

提示Hint

For the second test case, \(h(1) = h(2) = 2, h(3) = 3\).

出题Author

ftiasch

来源Source