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Josif_tepe

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Josif_tepe
Jun 23rd, 2025
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  1. #include <iostream>
  2. #include <bits/stdc++.h>
  3. #include <vector>
  4. using namespace std;
  5. const int maxn = 30005;
  6. const int INF = 2e9;
  7. int n;
  8. int A[maxn];
  9. int dp[maxn][4];
  10. int rec(int at, int medal) {
  11.     if(at == n) {
  12.         return 0;
  13.     }
  14.     if(dp[at][medal] != -1) {
  15.         return dp[at][medal];
  16.     }
  17.     int res = INF;
  18.     if(medal == 1) {
  19.         if(A[at] != medal) {
  20.             res = min(res, rec(at + 1, 1) + 1);
  21.             res = min(res, rec(at + 1, 2) + 1);
  22.             res = min(res, rec(at + 1, 3) + 1);
  23.         }
  24.         else {
  25.             res = min(res, rec(at + 1, 1));
  26.             res = min(res, rec(at + 1, 2));
  27.             res = min(res, rec(at + 1, 3));
  28.         }
  29.     }
  30.     else if(medal == 2) {
  31.         if(A[at] != medal) {
  32.             res = min(res, rec(at + 1, 2) + 1);
  33.             res = min(res, rec(at + 1, 3) + 1);
  34.         }
  35.         else {
  36.             res = min(res, rec(at + 1, 2));
  37.             res = min(res, rec(at + 1, 3));
  38.         }
  39.     }
  40.     else if(medal == 3) {
  41.         if(A[at] != medal) {
  42.             res = min(res, rec(at + 1, 3) + 1);
  43.         }
  44.         else {
  45.             res = min(res, rec(at + 1, 3));
  46.         }
  47.     }
  48.     dp[at][medal] = res;
  49.     return res;
  50. }
  51. int main() {
  52.     ios_base::sync_with_stdio(false);
  53.     cin >> n;
  54.    
  55.     for(int i = 0; i < n; i++) {
  56.         cin >> A[i];
  57.     }
  58.    
  59.     int res = INF;
  60.     memset(dp, -1, sizeof dp);
  61.     for(int i = 1; i <= 3; i++) {
  62.         res = min(res, rec(0, i));
  63.     }
  64.     reverse(A, A + n);
  65.     memset(dp, -1, sizeof dp);
  66.     for(int i = 1; i <= 3; i++) {
  67.         res = min(res, rec(0, i));
  68.     }
  69.     cout << res << endl;
  70.     return 0;
  71. }
  72.  
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