#include<bits/stdc++.h> using namespace std; #define ll long long #define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; i++) #define FORD(i, b, a) for (int i = (b), _a = (a); i >= _a; i--) #define pa pair<ll, ll> #define fi first #define se second #define bit(mask, j) ((mask >> j) & 1) const ll mod = 1e9 + 7; const ll INF = 1e18; //-------------------------------------------------------------------- ll s, t; ll n; const ll N = 2003; ll f[N][N][3]; ll calc(ll i, ll j, ll c) { if(i == n + 1) return j == 1; ll res = 0; if(f[i][j][c] != -1) return f[i][j][c]; if(i == s || i == t) { if(j != 0) res += calc(i + 1, j, c + 1); res += calc(i + 1, j + 1, c + 1); } else { res += calc(i + 1, j + 1, c) * (j + 1 - c); if(j >= 2) res += calc(i + 1, j - 1, c) * (j - 1); } return f[i][j][c] = res; } void hbmt() { memset(f, -1, sizeof f); cin >> n >> s >> t; cout << calc(1, 0, 0); } int main() { ios_base::sync_with_stdio(0); cin.tie(0);cout.tie(0); #define NAME "hbmt" if(fopen(NAME".inp", "r")) { freopen(NAME".inp", "r", stdin); freopen(NAME".out", "w", stdout); } //int t;cin>>t;while(t--) hbmt(); return 0; }

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:47:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   47 |                 freopen(NAME".inp", "r", stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:48:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   48 |                 freopen(NAME".out", "w", stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~