Codeforces 424 C. Magic Formulas

xor是满足交换律的,展开后发现仅仅要能高速求出 [1mod1....1modn],....,[nmod1...nmodn]的矩阵的xor即可了....然后找个规律

C. Magic Formulas

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

People in the Tomskaya region like magic formulas very much. You can see some of them below.

Imagine you are given a sequence of positive integer numbers p1, p2,
..., pn. Lets
write down some magic formulas:

Here, "mod" means the operation of taking the residue after dividing.

The expression  means
applying the bitwise xor (excluding "OR") operation to integers x and y.
The given operation exists in all modern programming languages. For example, in languages C++ and Java it is represented by "^", in Pascal — by "xor".

People in the Tomskaya region like magic formulas very much, but they don't like to calculate them! Therefore you are given the sequence p, calculate the
value of Q.

Input

The first line of the input contains the only integer n (1 ≤ n ≤ 106).
The next line contains n integers: p1, p2, ..., pn (0 ≤ pi ≤ 2·109).

Output

The only line of output should contain a single integer — the value of Q.

Sample test(s)

input

3
1 2 3

output

3

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>

using namespace std;

int XOR[1100000];

int main()
{
    int ans=0,n;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        int p;
        scanf("%d",&p);
        ans^=p;
    }
    for(int i=1;i<=n-1;i++)
    {
        XOR[i]=XOR[i-1]^i;
        int len=i+1;
        int res=n%(len*2);
        if(res>=len)
        {
            ans^=XOR[i];
            res-=len;
        }
        ans^=XOR[res];
    }
    printf("%d\n",ans);
    return 0;
}