离散化+预处理+分块，同题解做法

查出了无数个小错，可能是L，R的判定有锅

#include<bits/stdc++.h>
using namespace std;
int n, m, a[50005], b[50005], ans[305][305], cnt[50005][305], ll[305], rr[305], sum[50005], size;
int getL(int x)
{
	if(x % size == 0)
	{
		return x / size + 1;
	}
	else if(x % size == 1)
	{
		return x / size + 1;
	}
	return x / size + 2;
}
void init()
{
	ll[1] = 1;
	int tot = 1;
	size = sqrt(n);
	for(int i = 1; i <= n; i++)
	{
		if(i % size == 0)
		{
			rr[tot] = i;
			ll[++tot] = i + 1;
		}
	}
	rr[tot] = n;
	ll[tot + 1] = n + 1;
	rr[tot + 1] = n + 1;
	for(int i = 1; i <= tot; i++)
	{
		int st = ll[i], maxv = -0x3f3f3f3f, k = 0x3f3f3f3f;
		memset(sum, 0, sizeof(sum));
		for(int j = i; j <= tot; j++)
		{
			int ed = rr[j];
			while(st <= ed)
			{
				int v = ++sum[a[st]];
				if(v > maxv)
				{
					maxv = v;
					k = a[st];
				}
				else if(v == maxv && a[st] < k)
				{
					k = a[st];
				}
				st++;
			}
			ans[i][j] = k;
		}
	}
	memset(sum, 0, sizeof(sum));
	for(int i = 1; i <= tot; i++)
	{
		for(int j = 1; j <= n; j++)
		{
			cnt[a[j]][i] = cnt[a[j]][i - 1];
		}
		for(int j = ll[i]; j <= rr[i]; j++)
		{
			cnt[a[j]][i] = ++sum[a[j]];
		}
	}
	return;
}
int query(int l, int r)
{
	int maxv = -0x3f3f3f3f, k = 0x3f3f3f3f;
	memset(sum, 0, sizeof(sum));
	if(r - l < 2 * size)
	{
		for(int i = l; i <= r; i++)
		{
			int v = ++sum[a[i]];
			if(v > maxv)
			{
				maxv = v;
				k = a[i];
			}
			else if(v == maxv && a[i] < k)
			{
				k = a[i];
			}
		}
		return b[k];
	}
	int L = getL(l), R = r / size;
	k = ans[L][R];
	maxv = cnt[k][R] - cnt[k][L - 1];
	//cout << maxv << " " << R << " " << L-1 << endl;
	int st = rr[R], ed = ll[L];
	for(int i = l; i < ed; i++)
	{
		int v = ++sum[a[i]] + cnt[a[i]][R] - cnt[a[i]][L - 1];
		if(v > maxv)
		{
			maxv = v;
			k = a[i];
		}
		else if(v == maxv && a[i] < k)
		{
			k = a[i];
		}
	}
	for(int i = st + 1; i <= r; i++)
	{
		int v = ++sum[a[i]] + cnt[a[i]][R] - cnt[a[i]][L - 1];
		if(v > maxv)
		{
			maxv = v;
			k = a[i];
		}
		else if(v == maxv && a[i] < k)
		{
			k = a[i];
		}
	}
	return b[k];
}
int main()
{
	//freopen("P4168_1.in", "r", stdin);
	//freopen("P4168_1.ans", "w", stdout);
	cin >> n >> m;
	for(int i = 1; i <= n; i++)
	{
		cin >> a[i];
		b[i] = a[i];
	}
	sort(b + 1, b + n + 1);
	int ss = unique(b + 1, b + n + 1) - b;
	for(int i = 1; i <= n; i++)
	{
		a[i] = lower_bound(b + 1, b + ss + 1, a[i]) - b;
	}
	init();
	int l, r, last = 0;
	for(int i = 1; i <= m; i++)
	{
		cin >> l >> r;
		l = (l + last - 1) % n + 1;
		r = (r + last - 1) % n + 1;
		if(l > r)
		{
			swap(l, r);
		}
		last = query(l, r);
		cout << last << endl;
	}
	return 0;
}