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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4. typedef long double ld;
  5. typedef long long ll;
  6. typedef unsigned long long ull;
  7. const ll MAXN = 123456;
  8.  
  9. void pre();
  10. void post();
  11. ll n;
  12. string s;
  13.  
  14. void read()
  15. {
  16.     cin >> n;
  17.     cin >> s;
  18. }
  19.  
  20. int main()
  21. {
  22.     pre();
  23.     read();
  24.     ll maxans;
  25.     ll nowans;
  26.     bool now;
  27.     // if from 0 start
  28.     now = true;
  29.     nowans=0;
  30.     for(int i=0;i<n;i++)
  31.     {
  32.         if(now) {if(s[i]=='0'){now = !now;nowans++;}}
  33.         else {if(s[i]=='1'){now = !now;nowans++;}}
  34.     }
  35.     maxans = nowans;
  36.     // if from 1 start
  37.     now = false;
  38.     nowans=0;
  39.     for(int i=0;i<n;i++)
  40.     {
  41.         if(now) {if(s[i]=='0'){now = !now;nowans++;}}
  42.         else {if(s[i]=='1'){now = !now;nowans++;}}
  43.     }
  44.     maxans = max(maxans,nowans);
  45.  
  46.     vector<ll> blocks;
  47.     bool flag = s[0]=='0'?false:true;
  48.     bool startflag = flag;
  49.     blocks.push_back(0);
  50.     for(int i=0;i<n;i++)
  51.     {
  52.         if(flag && s[i]=='1')blocks[blocks.size()-1]++;
  53.         else if(!flag && s[i]=='0')blocks[blocks.size()-1]++;
  54.         else {flag = !flag;blocks.push_back(1);}
  55.     }
  56.     ll cntbolshe2=0;
  57.     for(int i=0;i<blocks.size();i++)
  58.     {
  59.         if(blocks[i]>=2)cntbolshe2++;
  60.     }
  61.     if(cntbolshe2>=2)
  62.     {
  63.         cout << maxans+2;
  64.         return 0;
  65.     }
  66.     for(int i=0;i<blocks.size();i++)
  67.     {
  68.         if(i<blocks.size()-1)
  69.         if(blocks[i]>=2 && blocks[i+1]>=2)
  70.         {
  71.             cout << maxans+2;
  72.             return 0;
  73.         }
  74.         if(i<blocks.size()-2)
  75.         if(blocks[i]>=2 && blocks[i+2]>=2)
  76.         {
  77.             cout << maxans+2;
  78.             return 0;
  79.         }
  80.         if(blocks[i]>=3)
  81.         {
  82.             cout << maxans+2;
  83.             return 0;
  84.         }
  85.     }
  86.     for(int i=0;i<blocks.size();i++)
  87.     {
  88.         if(blocks[i]>=2)
  89.         {
  90.             cout << maxans+1;
  91.             return 0;
  92.         }
  93.     }
  94.     cout << maxans;
  95.     /*if(s.find("0011")!=string::npos)
  96.     {
  97.         cout << maxans+2;
  98.     }
  99.     else if(s.find("011")!=string::npos || s.find("001")!=string::npos ||
  100.             s.find("111")!=string::npos || s.find("000")!=string::npos)
  101.     {
  102.         cout << maxans+1;
  103.     }
  104.     else cout << maxans;*/
  105.     post();
  106.     return 0;
  107. }
  108.  
  109.  
  110. void pre()
  111. {
  112. #ifdef DEBUG
  113.     freopen("input.txt", "r", stdin);
  114.     freopen("output.txt", "w", stdout);
  115. #endif
  116. }
  117.  
  118. void post()
  119. {
  120. #ifdef DEBUG
  121.     cerr << "Execution time: " << (ld) clock() / CLOCKS_PER_SEC;
  122. #endif
  123. }
Success #stdin #stdout 0s 3420KB
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https://ideone.com/sTgdE4
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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