题解 | 小红的三带一

//滑动窗口+哈希表+一点贪心
#include<iostream>
#include<vector>
#include<algorithm>
#include<unordered_map>
#define IOS ios::sync_with_stdio(false),cin.tie(nullptr),cout.tie(nullptr)
#define int long long
using namespace std;

void solve(){
   int cnt = 0;
   int n;
   cin >> n;
   vector<int>a(n);
   for(int i=0;i<n;i++)cin>>a[i];
   int l = 0;
   unordered_map<int,int>mp;
   for(int r = 0;r < n;r++){
      mp[a[r]]++;
      if(r - l + 1 > 4){
          mp[a[l]]--;
          if(mp[a[l]] == 0){
            mp.erase(a[l]);
          }
          l++;
      }
      if(r - l + 1 == 4){
        if(mp.size() == 2){
          bool f = false;
          for(auto&pair : mp){
            if(pair.second == 2){
              f = true;
              break;
            }
          }
          if(!f){
            cnt++;
            for(int i = l ; i <= r;i++){
              mp[a[i]]--;
              if(mp[a[i]] == 0){
                mp.erase(a[i]);
              }
              l = r+1;
            }
          }
        }
      }
   }cout<<cnt<<endl;
}
signed main(){
    IOS;
    int _ = 1;
    while(_--){
        solve();
    }
}