Sắp xếp THT Bảng B 2021

#include <iostream>
#include <algorithm>

using namespace std;
using ll = long long;

constexpr int N = 1e5 + 5;
constexpr int Inf = 999999999;

int n, s[N], p[N];
int a, b;

void Read()
{
    cin >> a >> b;

    for(int i = a; i <= b; ++i)
        s[++n] = i;
}

// Compare x and y
bool com(int x, int y) {
    string a, b;
    while(x) {
        a.push_back(char(x % 10 + '0'));
        x /= 10;
    }
    while(y) {
        b.push_back(char(y % 10 + '0'));
        y /= 10;
    }

    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());

    return a < b;
}

void Solve() {
    fill_n(p, N, Inf);
    p[0] = 0;
    int ans(0);

    for(int i = 1; i <= n; ++i) {
        int j = lower_bound(p + 1, p + n + 1, s[i], com) - p;

        ans = max(ans, j);
        if(com(s[i], p[j]))
            p[j] = s[i];
    }

    cout << n - ans;
}

int main ()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    Read();
    Solve();
}