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

B. Sereja and Stairs

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

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.

Sample test(s)

input

5
1 2 3 4 5

output

5
5 4 3 2 1

input

6
1 1 2 2 3 3

output

5
1 2 3 2 1

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#include<bits/stdc++.h>
#define M 100001
using namespace std;
int a[M],vis[5001], b[M];
int main()
{
    memset(vis,0,sizeof vis);
    int n,x,maxx=-1;
    scanf("%d",&n);
    for(int i=0;i<n;++i){
        scanf("%d",&x);
        vis[x]++;     //累计出现的次数
        if(x>maxx) maxx=x;  //找到最大的
    }
    int k=0,cnt=1;
    for(int i=0;i<maxx;++i){
        if(vis[i]>=2){  //如果比最大的小，而且出现次数大于2，那么可以放在前半部分
            cnt++;
            b[k++]=i;
            vis[i]--;  
        }
    }
    b[k++]=maxx;  
    for(int i=maxx-1;i>=0;--i){
        if(vis[i]){    //只要比最大的数小，而且有出现，就放到后半部分
            b[k++]=i;
            cnt++;
        }
    }
    cout<<cnt<<endl;
    for(int i=0;i<k;++i){
        cout<<b[i]<<" ";
    }
    cout<<endl;
    return 0;
}