AtCoderC - Colorful Candies map+双指针

Posted 2021-11-02 karshey

C

先看一则map的运用：

#include<bits/stdc++.h>
using namespace std;
map<int,int>mp;
int main()
{
	mp[1]=2;
	mp[2]=3;
	cout<<mp.size()<<endl;
	mp[1]=0;
	cout<<mp.size()<<endl;
	mp.erase(1);
	cout<<mp.size()<<endl;
	return 0; 
}
/*输出
2
2
1
*/

善用map的删除功能。然后就可以做这道题了。

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define pb push_back
#define fi first
#define se second
#define mem(a,x) memset(a,x,sizeof(a));
#define db double 
#define fir(i,a,n) for(int i=a;i<=n;i++)
//======================
const int N=3e5+10;
int a[N],b[N];//b[i] 以i为结尾的 
map<int,int>mp;
int ans=-1;
int n,k;
int main()
{
	cin>>n>>k;
	for(int i=1;i<=n;i++) cin>>a[i];
	for(int i=1;i<=k;i++)
	{
		mp[a[i]]++;
	}
	b[k]=mp.size();
	for(int i=k+1;i<=n;i++)
	{
		//1~k  2~k+1 到k+1即加k+1 减1(i-k)
		mp[a[i]]++;
		mp[a[i-k]]--;
		if(mp[a[i-k]]<=0)
		{
			mp.erase(a[i-k]);
		}
		b[i]=mp.size();
	}
	fir(i,k,n)
	{
		ans=max(ans,b[i]);
	}
	cout<<ans;
	return 0; 
}