CSUST 2009-Longest Subarray（队列的应用）

题目链接：http://acm.csust.edu.cn/problem/2009
博客园食用链接： https://www.cnblogs.com/lonely-wind-/p/13397273.html
Description

You are given two integers $C$, $K$ and an array of $N$ integers $a_1,a_2,\cdots,a_N$It is guaranteed that the value of $a_i$ is between $1$ to $C$

We define that a continuous subsequence $a_{l},a_{l+1},...,a_r(l \leq r)$ of array a is a good subarray if and only if the following condition is met:
$\forall x\in [1,C],\sum_{i=l}^{r}[a_i=x]\leq K$

It implies that if a number appears in the subarray, it will appear no greater than $K$ times.

You should find the longest good subarray and output its length. Or you should print $0$ if you cannot find any.

Input
Each case starts with a line containing three positive integers $N,K,C (1 \leq N,K,C \leq 300000)$

The second line contains $N$ integer $a_1,a_2,\cdots a_N(1\leq a_i\leq C)$

Output
For each test case, output one line containing an integer denoting the length of the longest good subarray.

Sample Input 1
5 1 3
1 2 3 1 2

Sample Output 1
3

emmm，CSUSTOJ为数不多的几道英文题面QWQ，实际上挺简单的。

题目大意：让你找到一个最长的的连续子序列，使得这个子序列中每个元素出现的次数小于等于 $K$。

既然是找连续的，那么这个就很简单了，一旦碰到出现次数大于 $K$的，我们将前面的元素一直往外抛就完事了，这不就是个队列的问题了嘛。

以下是AC代码：

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

const int mac=3e5+10;

int vis[mac],a[mac];

int main(int argc, char const *argv[])
{
	int n,k,c;
	scanf ("%d%d%d",&n,&k,&c);
	for (int i=1; i<=n; i++)
		scanf ("%d",&a[i]);
	int ans=0,j=1;
	for (int i=1; i<=n; i++){
		vis[a[i]]++;
		while (vis[a[i]]>k){
			vis[a[j]]--; j++;
		}
		ans=max(ans,i-j+1);
	}
	printf("%d\n",ans);
	return 0;
}