リストの実装

# 2021/03/15
# include <iostream>
# include <list>
using namespace std;

int main(void){
   list<int> x;
   
   for(int i=0;i<10;i++){
       x.push_back(i*3);
   }
   
   for(auto i = x.begin(); i != x.end(); i++){
       cout << *i << endl;
   }
   // 0
   // 3
   // 6
   // ...
   // 27
}

・最小公倍数(lcm)、最大公約数(gcd)

# include <iostream>
# include <numeric>
using namespace std;

int main(){
  cout << lcm(9,12) << endl;
  // 36
  cout << gcd(49,14) << endl;
  // 7
}

・next_permutation（順列全探索）(2021/05/12 : 色々間違ってたので訂正)

# include <iostream>
# include <vector>
# include <algorithm>
using namespace std;
int main(void){
   vector<int> a = {2,4,6};
   do{
       cout << a[0] << a[1] << a[2] << endl;
   }while(next_permutation(a.begin(), a.end()));
}
// 246
// 264
// 426
// 462
// 624
// 642

・文字列中の文字をカウント

# include <iostream>
using namespace std;
int main(void){
   string s = "atcoder_beginner_contest";
   cout << count(s.cbegin(),s.cend(),'e') << " ";
   cout << count(s.cbegin(),s.cend(),'t') << endl;
   // 4 3
}

・繰り返しニ乗法

long long modPow (long long x, long long y, long long MOD) {
    if (y == 0) return 1;
    if (y % 2 == 1) return (x * modPow(x, y-1, MOD)) % MOD;
    long long xx = modPow(x, y/2, MOD);
    return (xx * xx) % MOD;
}