Submission #443099

#	Time	Username	Problem	Language	Result	Execution time	Memory
443099		tranxuanbach	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	38 ms	15940 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;

#define endl '\n'
#define fi first
#define se second
#define For(i, l, r) for (int i = l; i < r; i++)
#define ForE(i, l, r) for (int i = l; i <= r; i++)
#define FordE(i, l, r) for (int i = l; i >= r; i--)
#define Fora(v, a) for (auto v: a)
#define bend(a) a.begin(), a.end()
#define isz(a) ((signed)a.size())

using ll = long long;
using ld = long double;
using pii = pair <int, int>;
using vi = vector <int>;
using vpii = vector <pii>;
using vvi = vector <vi>;

const int maxN = 2e3 + 5, mod = 1e9 + 7;

void sadd(int& x, int y){
    if ((x += y) >= mod) x -= mod; return;
}

int add(int x, int y){
    if ((x += y) >= mod) x -= mod; return x;
}

void ssub(int& x, int y){
    if ((x -= y) < 0) x += mod; return;
}

int sub(int x, int y){
    if ((x -= y) < 0) x += mod; return x;
}

int mul(int x, int y){
    return 1ll * x * y % mod;
}

int binpow(int x, int y){
    int ans = 1;
    while (y){
        if (y & 1) ans = mul(ans, x);
        x = mul(x, x);
        y >>= 1;
    }
    return ans;
}

int inv(int x){
    return binpow(x, mod - 2);
}

#define div __div__
int div(int x, int y){
    return mul(x, binpow(y, mod - 2));
}

int n, cs, cf;
int dp[maxN][maxN];

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    // freopen("KEK.inp", "r", stdin);
    // freopen("KEK.out", "w", stdout);
    cin >> n >> cs >> cf;
    dp[0][0] = 1;
    int cap = 0;
    ForE(i, 1, n){
        ForE(cc, 1, n){
            if (i == cs or i == cf){
                sadd(dp[i][cc], dp[i - 1][cc - 1]);
                sadd(dp[i][cc], dp[i - 1][cc]);
                continue;
            }
            sadd(dp[i][cc], mul(dp[i - 1][cc - 1], cc - cap));
            sadd(dp[i][cc], mul(dp[i - 1][cc + 1], cc));
        }
        if (i == cs or i == cf){
            cap++;
        }
    }
    cout << dp[n][1] << endl;
}

/*
==================================================+
INPUT:                                            |
--------------------------------------------------|

--------------------------------------------------|
==================================================+
OUTPUT:                                           |
--------------------------------------------------|

--------------------------------------------------|
==================================================+
*/

Compilation message (stderr)

kangaroo.cpp: In function 'void sadd(int&, int)':
kangaroo.cpp:27:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   27 |     if ((x += y) >= mod) x -= mod; return;
      |     ^~
kangaroo.cpp:27:36: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
   27 |     if ((x += y) >= mod) x -= mod; return;
      |                                    ^~~~~~
kangaroo.cpp: In function 'int add(int, int)':
kangaroo.cpp:31:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   31 |     if ((x += y) >= mod) x -= mod; return x;
      |     ^~
kangaroo.cpp:31:36: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
   31 |     if ((x += y) >= mod) x -= mod; return x;
      |                                    ^~~~~~
kangaroo.cpp: In function 'void ssub(int&, int)':
kangaroo.cpp:35:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   35 |     if ((x -= y) < 0) x += mod; return;
      |     ^~
kangaroo.cpp:35:33: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
   35 |     if ((x -= y) < 0) x += mod; return;
      |                                 ^~~~~~
kangaroo.cpp: In function 'int sub(int, int)':
kangaroo.cpp:39:5: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   39 |     if ((x -= y) < 0) x += mod; return x;
      |     ^~
kangaroo.cpp:39:33: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
   39 |     if ((x -= y) < 0) x += mod; return x;
      |                                 ^~~~~~

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