STL and templates quick reference

stl.cpp

#include <bits/stdc++.h> 
using namespace std;

// function template examples 
template <typename T> 
void print_vector(const vector<T>& temp){
  cout<<"{";
  for(int i=0;i<temp.size();i++){
    cout<<temp[i];
    if(i!= temp.size()-1)
      cout<<","; 
  }
  cout<<"}"<<"\n"; 
}

struct student{
    int id; 
    string name; 
    int rank; 
   
   /*
    bool operator<(const student& other){       //overload the "<" operator to support built-in sort, but what if we need different flavours 
        return id < other.id; 
    }
    */ 
    
    /*
    ostream& operator<<(ostream& os){
        os<<"ID: "<< id<<"\n"; 
        os<<"Name: "<<name<<"\n"; 
        os<<"Rank: "<<rank<<"\n"; 
        return os; 
    }
    */
}; 
bool cmp_by_rank(const student& a, const student& b){
    return a.rank < b.rank; 
}

bool cmp_by_id(const student& a, const student& b){
    return a.id < b.id; 
}

template<typename T> 
void swap_v(T& a, T& b){
  T temp; 
  temp = a; 
  a= b; 
  b = temp; 
}


template<typename T> 
T triple(T value){
    return value + value + value; 
}


template<typename T> 
T abs_max(T a, T b){
    return abs(a) > abs(b) ? a : b; 
}

template<typename T> 
struct Mychoices{
    T a, b,c,d; 
};

template<typename T> 
ostream& operator<<(ostream& os,const Mychoices<T>& t){         // overload how the object of type Mychoices, should be represented  
    os<<"A :"<< t.a<<"\n"; 
    os<<"B: "<<t.b<<"\n"; 
    os<<"C: "<<t.c<<"\n"; 
    os<<"D: "<<t.d<<"\n";
    return os; 
}

ostream& operator<<(ostream& os, const student& s){ // same as above, but now for our student object 
    os<<"Name: "<<s.name<<"\n"; 
    os<<"ID: "<<s.id<<"\n"; 
    os<<"Rank: "<<s.rank<<"\n"; 
    return os;
}
 



int main(){
    //templates  
    Mychoices<int>  choice1{1,2,3,4}; 
    cout<<choice1<<"\n";
    Mychoices<string> choice2{"megan fox", "kiera knighly" , "Gal gadot", "anne hathaway"}; 
    cout<<choice2<<"\n"; 
    
    vector<student> student_list; 
    
    student_list.push_back(student{4,"Priya ",1}); 
    student_list.push_back(student{5,"Kavitha",4}); 
    student_list.push_back(student{3,"kashyap",5}); 
    student_list.push_back(student{1,"kishore",2}); 
    student_list.push_back(student{2,"magesh",3}); 
    sort(student_list.begin(),student_list.end(),cmp_by_rank);  // sort by rank 
    
    print_vector(student_list);
    
    sort(student_list.begin(),student_list.end(),cmp_by_id);  // sort by id 
    print_vector(student_list); 
    
    
    
    
    vector<int> arr = {1,2,3,4,5,6,7}; 
    arr.push_back(11); 
    arr.push_back(9); 
    arr.push_back(3); 
    arr.push_back(3); 
    arr.push_back(3); 
    
    cout<<"before sorting :"; 
    
    print_vector(arr); 
    cout<<"after sorting : "; 
    
    sort(arr.begin(),arr.end()); 
    print_vector(arr); 
    int search_val = 10; 
    if(binary_search(arr.begin(),arr.end(), search_val )){ //return 0, if not found 
        cout<<"The value " <<search_val<<" is present"<<"\n"; 
    } 
    else{
        cout<<"The value is not found"<<"\n";
    }
    // upper bound and lower bound, the place where it can be inserted
    
    cout<<"upper bound for 10 " << upper_bound(arr.begin(),arr.end(), 10)- arr.begin()<<"\n"; // subtract it with begin iterator to get the index spot 
    cout<<"lower bound for 3"<<lower_bound(arr.begin(),arr.end(),3)- arr.begin()<<"\n";   
    

    // list - use it when you want to remove elements in constant time, 
    
    list<int> li = {4,5,6,7,6}; 
    li.remove(6); // removes all occurences of 6 
    for(auto i : li) cout<<i<<"\n";
    
    
    
    
    
    //set- like an always sorted array, will not contain duplicates  
    set<int> s = {5,4,3,2,1};  //initializer
    set<int>::iterator st; 
    cout<<"array sorted by set"<<"\n"; 
    for(st = s.begin(); st!= s.end();st++){       // similary we can just use auto to traverse 
        cout<<*st<<"\n"; 
    }
    // for(auto i: s) cout<<i<<"\n"; 
    s.insert(-1); 
    cout<<"new smallest element: "<<*s.begin()<<"\n"; 
    s.insert(7); 
    cout<<"new largest element: "<<*s.end()<<"\n";
    s.insert(8); 
    cout<<*s.lower_bound(6)<<"\n";  // smallest key greater than the value 
    
    
    
    // map 
    map<string,int> mp; 
    vector<string> words  ={"hello", "world","i" , "love" ,"apple","i" , "love","world", "i","love","kiera" }; 
    for(string i :words)
        mp[i]++; 
    for(auto i : mp){  // it returns a pair 
        cout<<i.first<<" "<<i.second<<"\n"; 
    }
    // find most repeated elements 
    int max_count= INT_MIN; 
    for(auto i: mp){
        max_count = max(max_count, i.second); 
        
    }
    vector<string> most_repeated; 
    for(auto i : mp){
        if(i.second == max_count){
            most_repeated.push_back(i.first); 
        }
    }
    print_vector(most_repeated); 
    
    int a{triple(3)}; 
    
    cout<<a<<"\n";
    string name{triple(string{"abc"})}; 
    cout<<name<<"\n"; 
    
    cout<<abs_max(5,4)<<"\n";
  
}

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