A - Remove Duplicates

integers. He wants to remove duplicate (equal) elements.

Petya wants to leave only the rightmost entry (occurrence) for each element of the array. The relative order of the remaining unique elements should not be changed.

The first line contains a single integer n

) — the number of elements in Petya's array.

The following line contains a sequence a1,a2,…,an

) — the Petya's array.

In the first line print integer x

— the number of elements which will be left in Petya's array after he removed the duplicates.

In the second line print x

integers separated with a space — Petya's array after he removed the duplicates. For each unique element only the rightmost entry should be left.

6
1 5 5 1 6 1

3
5 6 1 

5
2 4 2 4 4

2
2 4 

5
6 6 6 6 6

1
6 

In the first example you should remove two integers 1

.

In the second example you should remove integer 2

.

In the third example you should remove four integers 6

, which are in the positions 1, 2, 3 and 4.

AC代码（把数列到倒过来，然后记录第一个，倒着输出就可以了）

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main()
{
    int a[60], i, b[1000+10], c[60];
    int n, h;
    while(scanf("%d",&n)!=EOF)
    {
     memset(b, 0, sizeof(b));
     h = 0;
     for(i = 0;i<n;i++)
     {
      scanf("%d",&a[i]);
     }
     for(i = n-1;i>=0;i--)
     {
      if(b[a[i]]==0)
      {
       c[h++] = a[i];
      }
      b[a[i]]++;
     }
     printf("%d\n",h);
     for(i = h-1;i>=0;i--)
     printf("%d%c",c[i],i==0?'\n':' ');
    }
    return 0;
}