4471: Arpa’s obvious problem and Mehrdad’s terrible solution
题目描述
There are some beautiful girls in Arpa’s land as mentioned before.
Once Arpa came up with an obvious problem:
Given an array and a number x, count the number of pairs of indices i,j (1≤i<j≤n) such that 
, where 
is bitwise xor operation (see notes for explanation).
Immediately, Mehrdad discovered a terrible solution that nobody trusted. Now Arpa needs your help to implement the solution to that problem.
First line contains two integers n and x (1≤n≤105,0≤x≤105)− the number of elements in the array and the integer x.
Second line contains n integers a1,a2,...,an (1≤ai≤105)− the elements of the array.
Print a single integer: the answer to the problem.
2 3
1 2
1
6 1
5 1 2 3 4 1
2
In the first sample there is only one pair of i=1 and j=2. 
so the answer is 1.
In the second sample the only two pairs are i=3, j=4 (since 
) and i=1, j=5 (since 
).
A bitwise xor takes two bit integers of equal length and performs the logical xor operation on each pair of corresponding bits. The result in each position is 1 if only the first bit is 1 or only the second bit is 1, but will be 0 if both are 0 or both are 1. You can read more about bitwise xor operation here: https://en.wikipedia.org/wiki/Bitwise_operation#XOR.