AC题解：

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

long long f[11][2][10][2], cnt[11][2][10][2], ten[11] = {1};
bool vis[11][2][10][2];
int a[11];

void init() {
	for (int i = 1; i < 11; i++)
		ten[i] = ten[i-1] * 10;
}

long long dfs(int p, bool zero, int pre, bool limit) {
	if (p == 0) {
		int up = limit ? a[p] : 9;
		f[p][zero][pre][limit] = (1 + up) * up / 2;
		cnt[p][zero][pre][limit] = 1 + up;
		if (!zero && pre <= up) {
			f[p][zero][pre][limit] -= pre;
			cnt[p][zero][pre][limit]--;
		}
		return f[p][zero][pre][limit];
	}
	if (vis[p][zero][pre][limit])
		return f[p][zero][pre][limit];
	vis[p][zero][pre][limit] = true;
	int up = limit ? a[p] : 9;
	for (int i = 0; i <= up; i++) {
		if (!zero && i == pre)
			continue;
		dfs(p-1, zero && !i, i, limit && i == up);
		f[p][zero][pre][limit] += f[p-1][zero && !i][i][limit && i == up]
				+ i * ten[p] * cnt[p-1][zero && !i][i][limit && i == up];
		cnt[p][zero][pre][limit] += cnt[p-1][zero && !i][i][limit && i == up];
	}
	return f[p][zero][pre][limit];
}

long long cal(int num) {
	memset(cnt, 0, sizeof cnt);
	memset(f, 0, sizeof f);
	memset(vis, 0, sizeof vis);
	int p = 0;
	for (; num; a[p++] = num % 10, num /= 10) ;
	return dfs(p-1, true, 0, true);
}

int main() {
	init();
	int l, r;
	cin >> l >> r;
	cout << (long long) (l + r) * (r - l + 1) / 2 - cal(r) + cal(l-1) << endl;
	return 0;
}

WA代码：

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

long long f[11][2][10][2], cnt[11][2][10][2], ten[11] = {1};
bool vis[11][2][10][2];
int a[11];

void init() {
	for (int i = 1; i < 11; i++)
		ten[i] = ten[i-1] * 10;
}

long long dfs(int p, bool zero, int pre, bool limit) {
	if (p == 0) {
		int up = limit ? a[p] : 9;
		f[p][zero][pre][limit] = (1 + up) * up / 2;
		cnt[p][zero][pre][limit] = 1 + up;
		return f[p][zero][pre][limit];
	}
	if (vis[p][zero][pre][limit])
		return f[p][zero][pre][limit];
	vis[p][zero][pre][limit] = true;
	int up = limit ? a[p] : 9;
	for (int i = 0; i <= up; i++) {
		if (!zero && i == pre)
			continue;
		dfs(p-1, zero && !i, i, limit && i == up);
		f[p][zero][pre][limit] += f[p-1][zero && !i][i][limit && i == up]
				+ i * ten[p] * cnt[p-1][zero && !i][i][limit && i == up];
		cnt[p][zero][pre][limit] += cnt[p-1][zero && !i][i][limit && i == up];
	}
	return f[p][zero][pre][limit];
}

long long cal(int num) {
	memset(cnt, 0, sizeof cnt);
	memset(f, 0, sizeof f);
	int p = 0;
	for (; num; a[p++] = num % 10, num /= 10) ;
	return dfs(p-1, true, 0, true);
}

int main() {
	init();
	int l, r;
	cin >> l >> r;
	cout << (long long) (l + r) * (r - l + 1) / 2 - cal(r) + cal(l-1) << endl;
	return 0;
}