[Codeforce Round #242]C. Magic Formulas

題目網址: http://codeforces.com/contest/424/problem/C

題意: 題目給定公式，計算答案。



解法: 利用xor的交換律，及mod的規律，即可快速計算答案。

TAG: math

程式碼:

	#include <iostream>
	#include <cstdio>
	#include <cstring>
	using namespace std;
	int n;
	int q;
	int xx[1000005];
	int cal( int val )
	{
	static int i, ret;
	ret = 0;
	if( (n/val)&1 ) {
	ret ^= xx[val-1];
	}
	ret ^= xx[n%val];
	return ret;
	}
	int main( void )
	{
	int i, x;
	xx[0] = 0;
	for( i = 1; i <= 1000000; ++i ) xx[i] = xx[i-1]^i;
	while( scanf( "%d", &n ) == 1 ) {
	q = 0;
	for( i = 1; i <= n; ++i ) {
	scanf( "%d", &x );
	q ^= x;
	q ^= cal(i);
	}
	printf( "%d\n", q );
	}
	return 0;
	}

view raw Magic Formulas.cpp hosted with ❤ by GitHub