Codeforces Round #223 (Div. 2) B. Sereja and Stairs

Sereja loves integer sequences very much. He especially likes stairs.

Sequence a1, a2, ..., a|a| (|a| is
the length of the sequence) is stairs if there is such index i (1 ≤ i ≤ |a|),
that the following condition is met:
a1 < a2 < ... < ai - 1 < ai > ai + 1 > ... > a|a| - 1 > a|a|.

For example, sequences [1, 2, 3, 2] and [4, 2] are stairs and sequence [3, 1, 2] isn't.

Sereja has m cards with numbers. He wants to put some cards on the table in a row to get a stair sequence. What maximum number of cards can he put on the
table?

Input

The first line contains integer m (1 ≤ m ≤ 105) —
the number of Sereja's cards. The second line contains m integers bi (1 ≤ bi ≤ 5000) —
the numbers on the Sereja's cards.

Output

In the first line print the number of cards you can put on the table. In the second line print the resulting stairs.

输出数列为凸型

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int cmp ( const void *a , const void *b ) { return *(int *)a - *(int *)b; }

int main()
{
int a[100010],b[100010],c[100010],n,i,j,x=0;
scanf("%d",&n);
for(int k=0;k<n;++k)
scanf("%d",&a[k]);
qsort(a,n,sizeof(int),cmp);

memset(b,0,sizeof(b));

i=0;j=n-1;

x=n;
for(int k=0;k<n;)
{
if(a[k]==b[i-1]&&a[k]==b[j+1]) {++k;--x;continue;}
if(a[k]!=b[i-1])
b[i++]=a[k++];
else b[j--]=a[k++];
}
if(b[i-1]==b[j+1])
{
b[j+1]=0;
--x;
}

printf("%d\n",x);

for(int k=n-1;k>0;--k)
if(b[k])
printf("%d ",b[k]);

printf("%d\n",b[0]);

return 0;
}