Submission #439724

#	Time	Username	Problem	Language	Result	Execution time	Memory
439724		stoyan_malinin	Rack (eJOI19_rack)	C++14	100 / 100	5 ms	292 KiB

rack

#include <iostream>

using namespace std;

const long long mod = 1e9 + 7;

long long fastPow(long long x, long long p)
{
    long long ans = 1, curr = x;

    while(p!=0)
    {
        if(p%2!=0) ans = (ans*curr)%mod;

        p/=2;
        curr = (curr*curr)%mod;
    }

    return ans;
}

long long walkLeft(long long node, int layer, int n)
{
    if(layer==n+1) return node%mod;
    return walkLeft((node*2)%mod, layer+1, n);
}

long long revNum(long long x, int bitCnt)
{
    long long res = 0;
    for(int bit = 0;bit<bitCnt;bit++)
        res += (((x>>bit)&1)<<(bitCnt-bit-1));
    
    return res;
}

int main()
{
    long long n, k;
    cin >> n >> k;

    if(k==1)
    {
        cout << "1" << '\n';
        return 0;
    }
    k--;

    int layer;
    for(layer = 1;layer<=n;layer++)
    {
        long long maxNum = (1LL<<(layer)) - 1;
        if(k<=maxNum) break;
    }   

    long long start = (1LL<<(layer-1));
    long long kLeft = k - ((1LL<<(layer-1)) - 1) - 1;
    long long node = start + revNum(kLeft, layer-1);

    node %= mod;
    cout << (walkLeft(node*2+1, layer+1, n) - fastPow(2, n) + 1 + mod)%mod << '\n';
}

• Subtask 1: 20 / 20
• Subtask 2: 20 / 20
• Subtask 3: 60 / 60