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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define int              long long int
  4. #define double           long double
  5. #define print(a)         for(auto x : a) cout << x << " "; cout << endl
  6.  
  7.  
  8. const int M = 1000000007;
  9. const int N = 3e5+9;
  10. const int INF = 2e9+1;
  11. const int LINF = 2000000000000000001;
  12.  
  13.  
  14.  
  15. inline int power(int a, int b, int mod) {
  16.     int x = 1;
  17.     a %= mod;
  18.     while (b) {
  19.         if (b & 1) x = (x * a) % mod; 
  20.         a = (a * a) % mod;
  21.         b >>= 1;
  22.     }
  23.     return x;
  24. }
  25.  
  26.  
  27.  
  28. vector<int> fact(N);
  29. vector<int> ifact(N);
  30.  
  31.  
  32. void computeFactorial(int mod){
  33. 	fact[0] = ifact[0] = 1;
  34. 	for(int i=1; i<N; i++){
  35. 		fact[i] = (fact[i-1] * i)% mod;
  36. 	}
  37.  
  38.  
  39. 	ifact[N-1] = power(fact[N-1], mod-2, mod);
  40. 	for(int i = N-2; i>=1; i--){
  41. 		ifact[i] = (ifact[i+1] * (i+1))%mod;
  42. 	}
  43. }
  44.  
  45. int nCr(int n, int r, int mod){
  46. 	if(r>n || r<0) return 0;
  47. 	return ( ( fact[n] * ifact[r] )%mod * ifact[n-r] ) % mod;
  48. }
  49.  
  50.  
  51.  
  52. //_ ***************************** START Below *******************************
  53.  
  54.  
  55. int MOD = 998244353;
  56.  
  57.  
  58. vector<int> a;
  59.  
  60. int consistency(int n){
  61.  
  62.     computeFactorial(MOD);
  63.  
  64.     int ways = 1;
  65.     for(int i=0; i<=n-3; i+=3){
  66.         vector<int> triad = {a[i], a[i+1], a[i+2]};
  67.         sort(begin(triad), end(triad), greater<int>());
  68.  
  69.         if(triad[0] == triad[2]){
  70.             ways = (ways*3)%MOD;
  71.         }
  72.         else if(triad[0] != triad[1] && triad[1] == triad[2] ){
  73.             ways = (ways*2)%MOD;
  74.         }
  75.         else ways *= 1;
  76.     }
  77.  
  78.     int t = n/3; // total triads t
  79.     int totalWays = (nCr(t, t/2, MOD) * ways)%MOD;
  80.  
  81.  
  82.     return totalWays;
  83. }
  84.  
  85.  
  86.  
  87.  
  88.  
  89.  
  90.  
  91.  
  92.  
  93.  
  94.  
  95.  
  96.  
  97.  
  98.  
  99. int practice(int n){
  100.  
  101.  
  102.     return 0;
  103. }
  104.  
  105.  
  106.  
  107.  
  108.  
  109. void solve() {
  110.  
  111.     int n;
  112.     cin>> n;
  113.  
  114.     a.resize(n);
  115.     for(int i=0; i<n; i++) cin >> a[i];
  116.  
  117.     cout << consistency(n) << endl;
  118.  
  119.  
  120. }
  121.  
  122.  
  123.  
  124.  
  125.  
  126. int32_t main() {
  127.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  128.  
  129.     int t = 1;
  130.     // cin >> t;
  131.     while (t--) {
  132.         solve();
  133.     }
  134.  
  135.     return 0;
  136. }
Success #stdin #stdout 0.01s 7760KB
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https://ideone.com/MxyjrC
language:
C++14 (gcc 8.3)
created:
3 days ago
visibility:
public

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