Submission #95270

#	Time	Username	Problem	Language	Result	Execution time	Memory
95270		rkocharyan	Palindrome-Free Numbers (BOI13_numbers)	C++14	81.25 / 100	18 ms	444 KiB

numbers

#include <bits/stdc++.h>

using namespace std;

const int N = 20;

int n;
long long dp[N][2];
string s;

long long calc(int pos, int f, int c1, int c2, int c3) {
    if((c2 == c3 && c2 != -1 && c3 != -1) || (c1 == c3 && c1 != -1 && c3 != -1)) return 0;
    if(pos == n) return 1;
    auto &res = dp[pos][f];
    if(res != -1) {
        return res;
    }
    res = 0;
    int lmt = f ? 9 : s[pos] - '0';
    for(int i = 0; i <= lmt; i++) {
        int nf = f;
        if(i < lmt) nf = 1;
        res += calc(pos + 1, nf, c2, c3, i);
    }
    return res;
}

long long solve(string &x) {
    s = x;
    n = (int) x.size();
    memset(dp, -1, sizeof dp);
    return calc(0, 0, -1, -1, -1);
}

bool check(long long x) {
    string s = to_string(x);
    int m = (int) s.size();
    for(int i = 0; i < m - 1; i++) {
        if(s[i] == s[i + 1]) {
            return 0;
        }
    }
    for(int i = 0; i < m - 2; i++) {
        if(s[i] == s[i + 2]) {
            return 0;
        }
    }
    return 1;
}

long long brute(long long l, long long r) {
    int ans = 0;
    for(long long i = l + 1; i <= r; i++) {
        ans += check(i);
    }
    return ans;
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    long long l, r;
    cin >> l >> r;
    l--;
    string a, b;
    a = to_string(l);
    b = to_string(r);
    if(l == -1) {
        cout << solve(b) + 1 << '\n';
        return 0;
    }
    if(r - l <= 1e6) {
        cout << brute(l, r) << '\n';
    } else {
        cout << solve(b) - solve(a) << '\n';
    }
    return 0;
}

• Subtask 1: 21.25 / 25
• Subtask 2: 60 / 75