Jessica's Reading Problem

Jessica's Reading Problem

SCUACM2022集训前训练-数据结构 - Virtual Judge (vjudge.net)

双指针

假设当前枚举的区间是 $[l,r]$, 且是以 $r$ 为右端点的最大的可以满足条件的 $l$, 那么 $r++$ 时这个 $l$ 肯定还能满足条件，所以 $l$ 不会回退，可以用双指针

用 map 记录当前区间是否能覆盖所有知识点 (now.size() == m), 当某一个知识点的次数为 0 时，在 map 里删去

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>
#include <map>
using namespace std;
typedef long long ll;
const int N = 1e6 + 10;
int n;
int a[N];

int main()
{
	scanf("%d\n", &n);
	map<int, int> alls;
	for (int i = 1; i <= n; i++)
	{
		scanf("%d", a + i);
		alls[a[i]]++;
	}
	int m = alls.size();
	int ans = n;
	map<int, int> now;
	
	for (int l = 1, r = 1; r <= n; r++)
	{
		now[a[r]]++;
		while(l <= r && now.size() == m)
		{
			ans = min(ans, r - l + 1);
			now[a[l]]--;
			if (now[a[l]] == 0)
				now.erase(a[l]);
			l++;
		}
	}
	printf("%d\n", ans);
	return 0;
}