Submission #523738

#	Time	Username	Problem	Language	Result	Execution time	Memory
523738		LptN21	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	38 ms	15964 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;
#define fastIO ios_base::sync_with_stdio(false), cin.tie(NULL);
#define PI acos(-1.0)
#define eps 1e-9
#define FF first
#define SS second
// VECTOR (6)
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define sz(v) int((v).size())
#define all(v) (v).begin(), (v).end()
#define uniq(v) sort(all( (v) )), (v).resize( unique(all( (v) )) - (v).begin() );
// BIT (6)
#define CNTBIT(x) __builtin_popcountll(x)
#define ODDBIT(x) __builtin_parityll(x)
#define MASK(i) (1LL<<(i))
#define BIT(x, i) (((x)>>(i))&1)
#define SUBSET(big, small) (((big)&(small))==(small))
#define FIRSTBIT(x) __builtin_ctzll(x)
//typedef
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> ii;

/* */
template<class T>
bool minimize(T &a, const T &b) {
    if(a > b) {a = b; return 1;}
    return 0;
}
template<class T>
bool maximize(T &a, const T &b) {
    if(a < b) {a = b; return 1;}
    return 0;
}
/* */

/* CODE BELOW */
const int N = 2e3 + 7, M = 1e9 + 7;
const int oo = 1e9 + 7;
const int MOD = 1e9 + 7;

int n, cs, cf;

int _dp[N][N];

int add(int a, int b) {
    a+= b; if(a>=MOD) a-=MOD;
    return a;
}
int mul(int a, int b) {
    return (1LL * a * b)%MOD;
}
void update(int &a, int b) {
    a+= b; if(a>=MOD) a-=MOD;
}

signed main() {
    //freopen("test.inp", "r", stdin);
    //freopen("test.out", "w", stdout);
    //fastIO;
    scanf("%d%d%d", &n, &cs, &cf);
    _dp[1][1] = 1;
    for(int i=1;i<=n;i++) {
        for(int j=1;j<=n;j++) {
            if(i == cs || i == cf) {
                update(_dp[i][j], add(_dp[i-1][j-1], _dp[i-1][j]));
                // create new component
                // make it an endpoint of left/right component (based on whether it is cs of cf)
                continue;
            }
            update(_dp[i][j], mul(_dp[i-1][j-1], j - (i > cs) - (i > cf))); // create new component
            update(_dp[i][j], mul(_dp[i-1][j+1], j)); // connect 2 existing component
        }
    }
    printf("%d", _dp[n][1]);

    return 0;
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:65:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   65 |     scanf("%d%d%d", &n, &cs, &cf);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

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