Submission #988371

#	Time	Username	Problem	Language	Result	Execution time	Memory
988371		GrindMachine	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	37 ms	31836 KiB

kangaroo

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl

#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)

template<typename T>
void amin(T &a, T b) {
    a = min(a,b);
}

template<typename T>
void amax(T &a, T b) {
    a = max(a,b);
}

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif

/*

refs:
https://codeforces.com/blog/entry/47764?#comment-704139

*/

const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;

void solve(int test_case)
{
    ll n,cs,cf; cin >> n >> cs >> cf;
    ll dp[n+5][n+5];
    memset(dp,0,sizeof dp);
    dp[1][0] = 1;

    rep1(i,n){
        rep(j,n+1){
            dp[i][j] %= MOD;

            if(i == cs or i == cf){
                ll ways = j;
                if(i > min(cs,cf)){
                    if(i != n){
                        ways--;
                    }
                }

                // new
                dp[i+1][j+1] += dp[i][j];

                // merge
                dp[i+1][j] += dp[i][j]*ways;
            }
            else{
                // new
                dp[i+1][j+1] += dp[i][j];

                // merge
                if(j){
                    ll ways = 0;
                    ll spl = 0;

                    // cs on the left
                    if(i > cs){
                        ways += j-1;
                        spl++;
                    }

                    // cf on the right
                    if(i > cf){
                        ways += j-1;
                        spl++;
                    }

                    // cs on left, cf on right
                    if(spl == 2){
                        if(i == n) ways--;
                        else ways -= 2;
                    }

                    // no spl on both sides
                    ll non_spl = j-spl;
                    if(non_spl >= 2){
                        ways += non_spl*(non_spl-1);
                    }

                    dp[i+1][j-1] += ways*dp[i][j];
                }
            }
        }
    }

    ll ans = dp[n+1][1];
    cout << ans << endl;
}

int main()
{
    fastio;

    int t = 1;
    // cin >> t;

    rep1(i, t) {
        solve(i);
    }

    return 0;
}

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 49 / 49