poj3239

构造法。

// https://www.cnblogs.com/rainydays/archive/2011/07/12/2104336.html

#include 
#include 
#include 
#include 
using namespace std;

int n;

int main()
{
//freopen("t.txt", "r", stdin);
while (scanf("%d", &n), n)
{
if (n %6!=2&& n %6!=3)
{
printf("2");
for (int i =4; i <= n; i +=2)
printf(" %d", i);
for (int i =1; i <= n; i +=2)
printf(" %d", i);
putchar('\n');
continue;
}
int k = n /2;
printf("%d", k);
if (!(k &1) &&!(n &1))
{
for (int i = k +2; i <= n; i +=2)
printf(" %d", i);
for (int i =2; i <= k -2; i +=2)
printf(" %d", i);
for (int i = k +3; i <= n -1; i +=2)
printf(" %d", i);
for (int i =1; i <= k +1; i +=2)
printf(" %d", i);
}
else if (!(k &1) && (n &1))
{
for (int i = k +2; i <= n -1; i +=2)
printf(" %d", i);
for (int i =2; i <= k -2; i +=2)
printf(" %d", i);
for (int i = k +3; i <= n -2; i +=2)
printf(" %d", i);
for (int i =1; i <= k +1; i +=2)
printf(" %d", i);
printf(" %d", n);
}
else if ((k &1) &&!(n &1))
{
for (int i = k +2; i <= n -1; i +=2)
printf(" %d", i);
for (int i =1; i <= k -2; i +=2)
printf(" %d", i);
for (int i = k +3; i <= n; i +=2)
printf(" %d", i);
for (int i =2; i <= k +1; i +=2)
printf(" %d", i);
}
else if ((k &1) && (n &1))
{
for (int i = k +2; i <= n -2; i +=2)
printf(" %d", i);
for (int i =1; i <= k -2; i +=2)
printf(" %d", i);
for (int i = k +3; i <= n -1; i +=2)
printf(" %d", i);
for (int i =2; i <= k +1; i +=2)
printf(" %d", i);
printf(" %d", n);
}
putchar('\n');
}
return 0;
}

代码来自https://www.cnblogs.com/rainydays/archive/2011/07/12/2104336.html。