#F1003. Arpa’s obvious problem and Mehrdad’s terrible solution
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.
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