C :

#include<stdio.h>
#include<math.h>
#include<string.h>
typedef struct queue {
  int data;
  struct queue *next;
} linknode;
  linknode *front, *rear;
void iniqueue() {
  front= (linknode *) malloc(sizeof(linknode));
  front->next = NULL;
  rear = front;
}
void push( int x) {
  linknode *newq;
  newq = (linknode *) malloc(sizeof(linknode));
  newq->data = x;
  newq->next = NULL;
  rear->next = newq;
  rear = newq;
}
void pop() {
  linknode *pops;
  if (front->next != NULL) {
    pops = front->next;
    front->next = pops->next;
    free(pops);
  } else
    rear = front;
}
int search(int x) {
  linknode *sear;
  sear = front->next;
  while (sear != NULL) {
    if (sear->data == x)
      return 1;
    sear = sear->next;
  }
  return 0;
}
int main() {
  iniqueue();
  int m, n, nn;
  scanf("%d%d", &m, &n);
  int a[n];
  nn = n;
  for (int i = 0; i < n; i++)
    scanf("%d", &a[i]);
  int count = 0, ci = 0, j = 0;
  while (nn) {
    if (search(a[j]))
    {
        
      j++;
    } else {
    	  
      if (ci >= m) {
        pop();
        push(a[j]);
        ci++;
        j++;
        count++;
      }else {  
      push (a[j] );
      ci++;
      j++;
      count++;
      }
    }
      nn--;
  }

  printf("%d\n", count);
  return 0;
}

C++ :

#include <iostream>
#include <cstring>
#include <queue>

using namespace std;

#define N 1010

int main()
{
	queue<int> q;
	bool szExist[N] = {false};
	int nMem = 0;
	int nPassage = 0;
	int nWord = 0;
	int nCount = 0;
	memset(szExist, false, N);
	
	cin >>nMem >>nPassage;
	for (int i = 0; i < nPassage; ++i)
	{
		cin >>nWord;
		if (!szExist[nWord]) // 单词没有在内存中
		{
			++nCount;
			q.push(nWord);
			szExist[nWord] = true;
			if (q.size() > nMem)
			{
				szExist[q.front()] = false;
				q.pop();
			}
		}
	}
	
	cout <<nCount;
	
	return 0;
}

Java :

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner cin = new Scanner(System.in);
		int cap = cin.nextInt(),num = cin.nextInt();
		int count = 0;
		Queue<Integer> queue = new LinkedList<Integer>();
		for(int i = 0; i < num; i ++) {
			int temp = cin.nextInt();
			if(!queue.contains(temp) && queue.size()<cap) {
				queue.add(temp);
				count ++;
			}
			else if(!queue.contains(temp) && queue.size() == cap) {
				queue.poll();
				queue.add(temp);
				count ++;
			}
		}
		System.out.println(count);
	}
}