2015 Multi-University Training Contest 5 B（MZL's xor）

Problem Description
MZL loves xor very much.Now he gets an array A.The length of A is n.He wants to know the xor of all (Ai+Aj)(1≤i,j≤n)
The xor of an array B is defined as B1 xor B2...xor Bn
 

Input
Multiple test cases, the first line contains an integer T(no more than 20), indicating the number of cases.
Each test case contains four integers:n,m,z,l
A1=0,Ai=(Ai−1∗m+z) mod l
1≤m,z,l≤5∗105,n=5∗105
 

Output
For every test.print the answer.
 

Sample Input
2
3 5 5 7
6 8 8 9
 

Sample Output
14
16

题意：英语很短，不说了。

思路：(a1+a1)^(a1+a2)^(a1+a3)^...(an+an)^

                         (a2+a1)^(a3+a1)....

            其实这样就很明显了所有异或满足结合律，那么(ai+aj)^(aj+ai)=2(ai^aj)，那么看代码吧

int main()
{
    ll n , m , l , z ;
    int t ;
    scanf("%d" , &t) ;
    while(t--)
    {
        scanf("%I64d%I64d%I64d%I64d" , &n , &m , &z, &l) ;
        ll ans = 0 ;
        ll pre = 0 ;
        ll now ;
        for(int i = 2;i <= n;i++)
        {
           now = (pre*m + z)%l ;
           ans = ans^(2*now) ;
           pre = now ;
        }
       printf("%I64d\n" , ans) ;
    }
}