ST表

把每一段相同的数抽象成一个数，这个数的权值就是他出现的次数

code

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

namespace syr
{
	const ll N = 1e5+10;
	ll n, m, l, r, cnt;
	ll a[N], t[N], x[N], y[N], st[N][25];
	ll find (ll l, ll r) {
		if (r<l) return 0;
		ll k = log2(r-l+1);
		return max(st[l][k], st[r-(1<<k)+1][k]);
	}
	void work()
	{
		while (cin>>n) {
			if (!n) return;
			cin>>m;
			for (ll i=1; i<=n; i++) cin>>a[i];
			l = r = 1;
			while (r<=n) {
				cnt++;
				while (a[r]==a[l] && r<=n) {
					t[r] = cnt;
					r++;
				}
				x[cnt] = l;
				y[cnt] = r-1;
				st[cnt][0] = r-l;
				l = r;			
			}
			for (ll i=1; i<=21; i++)
				for (ll j=1; j+(1<<(i-1))<=cnt; j++)
					st[j][i] = max(st[j][i-1], st[j+(1<<(i-1))][i-1]);
			while (m--) {
				cin>>l>>r;
				if (t[l]==t[r]) {
					cout<<r-l+1<<'\n';
					continue;
				}
				ll ans=0;
				ans = max(y[t[l]]-l+1, r-x[t[r]]+1);
				ans = max(ans, find(t[l]+1, t[r]-1));
				cout<<ans<<'\n';
			}
		}
	}
} 

int main()
{
	cin.tie(0)->sync_with_stdio(0);
	syr::work();
	return 0;
}