rt,写了一坨分块一遍过阳历就交了上去，Code:

# include <bits/stdc++.h>

# define I return

# define AK 0

# define IOI ;

using namespace std;

typedef long long ll;

typedef pair <int, int> pii;

int n, m, op, l, r, t, col[50005], st[230], ed[230], lazy[230], s[230][30], a[50005];

string str;

char c;

void init () {

	t = sqrt (n);

	for (int i = 1; i <= t; ++ i)
		st[i] = n / t * (i - 1) + 1, ed[i] = n / t * i;

	ed[t] = n;

	for (int i = 1; i <= t; lazy[i] = -1, ++ i)
		for (int j = st[i]; j <= ed[i]; ++ j)
			col[j] = i, ++ s[i][a[j] - 'a'];

	return ;

}

void pushdown (int x) {

	if (~lazy[x]) {

		for (int i = st[x]; i <= ed[x]; ++ i)
			a[i] = lazy[x];

		lazy[x] = -1;

	}

	return ;

}

int find (const int l, const int r, const int k) {

	const int cl = col[l], cr = col[r];

	int sum = 0;

	pushdown (cl);

	if (cl == cr) {

		for (int i = l; i <= r; ++ i)
			sum += (a[i] == k);

		return sum;

	}

	for (int i = l; i <= ed[cl]; ++ i)
		sum += (a[i] == k);

	for (int i = cl + 1; i < cr; ++ i)
		sum += s[i][k];

	pushdown (cr);

	for (int i = st[cr]; i <= r; ++ i)
		sum += (a[i] == k);

	return sum;

}

void change (const int l, const int r, const int k) {

	const int cl = col[l], cr = col[r];

	pushdown (cl);

	if (cl == cr) {

		for (int i = l; i <= r; ++ i)
			-- s[cl][a[i]], ++ s[cl][k], a[i] = k;

		return ;

	}

	for (int i = l; i <= ed[cl]; ++ i)
		-- s[cl][a[i]], ++ s[cl][k], a[i] = k;

	for (int i = cl + 1; i < cr; ++ i) {

		for (int j = 0; j < 26; ++ j)
			s[i][j] = 0;

		s[i][k] = ed[i] - st[i] + 1;

		lazy[i] = k;

	}

	pushdown (cr);

	for (int i = st[cr]; i <= r; ++ i)
		-- s[cr][a[i]], ++ s[cr][k], a[i] += k;

	return ;

}

void sort (int l, int r) {

	const int cl = col[l], cr = col[r];

	pushdown (cl);

	if (cl == cr) {

		sort (a + l, a + r + 1);

		return ;

	}

	int sum[30] = {}, now = 0;

	for (int i = l; i <= ed[cl]; ++ i)
		++ sum[a[i]];

	for (int i = cl + 1; i < cr; ++ i)
		for (int j = 0; j < 26; ++ j)
			sum[j] += s[i][j];

	pushdown (cr);

	for (int i = st[cr]; i <= r; ++ i)
		++ sum[a[i]];

	for (int i = l; i <= ed[cl]; ++ i) {

		-- s[cl][a[i]], ++ s[cl][now], a[i] = now, -- sum[now];

		while (now < 26 && ! sum[now])
			++ now;

	}

	for (int i = cl + 1; i < cr; ++ i)
		if (sum[now] >= ed[i] - st[i] + 1) {

			for (int j = 0; j < 26; ++ j)
				s[i][j] = 0;

			s[i][now] = ed[i] - st[i] + 1;

			sum[now] -= ed[i] - st[i] + 1;

			lazy[i] = now;

			while (now < 26 && ! sum[now])
				++ now;

		} else for (int j = st[i]; j <= ed[i]; ++ j) {

				-- s[cr][a[j]], ++ s[cr][now], a[j] = now, -- sum[now];

				while (now < 26 && ! sum[now])
					++ now;

			}

	for (int i = st[cr]; i <= r; ++ i) {

		-- s[cr][a[i]], ++ s[cr][now], a[i] = now, -- sum[now];

		while (now < 26 && ! sum[now])
			++ now;

	}

	return ;

}

int main () {

	ios::sync_with_stdio (0);

	cin.tie (0);

	cout.tie (0);

	cin >> n >> m >> str;

	for (int i = 0; i < n; ++ i)
		a[i + 1] = str[i] >= 'a' ? str[i] - 'a' : str[i] - 'A';

	init ();

	while (m --) {

		cin >> op >> l >> r;

		if (op < 2)
			cin >> c, cout << find (l, r, c >= 'a' ? c - 'a' : c - 'A') << '\n';
		else if (op < 3)
			cin >> c, change (l, r, c >= 'a' ? c - 'a' : c - 'A');
		else
			sort (l, r);

	}

	I AK IOI

}