Question

How to find the largest three elements in a vector with C++

Answer 1

#include <iostream>
#include <algorithm> 
#include <vector>

int main()
{
    std::vector<int> v = { 5, 2, 9, 6, 12, 7, 8, 3, 1, 0 };
    
    partial_sort(v.begin(), v.begin() + 3, v.end(), std::greater<int>());
 
    for(auto const& n : v)
        std::cout << n << " ";
        
    std::cout << "\nfirst = " << v[0] << "\n";
    std::cout << "second = " << v[1] << "\n";
    std::cout << "third = " << v[2] << "\n";

    return 0;
}



/*
run:
       
12 9 8 2 5 6 7 3 1 0 
first = 12
second = 9
third = 8
       
*/

 

 

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Answer 2

#include <iostream>
#include <vector>
#include <climits>
 
void print3largest(std::vector<int> v) { 
    int size = v.size();
    if (size < 3) { 
        std::cout << "vector size < 3"; 
        return; 
    } 
     
    int first, second, third; 
    
    third = first = second = INT_MIN;
 
    for (int i = 0; i < size ; i ++) { 
        if (v[i] > first) { 
            third = second; 
            second = first; 
            first = v[i]; 
        } 
        else if (v[i] > second) { 
            third = second; 
            second = v[i]; 
        } 
        else if (v[i] > third) 
            third = v[i]; 
    } 
    std::cout << "The three largest elements are: " << first << " " << second << " " << third; 
} 
    
    
int main() 
{ 
    std::vector<int> v = { 5, 2, 9, 6, 12, 7, 8, 3, 1, 0 };

    print3largest(v); 
     
    return 0; 
} 
 
 
 
 
/*
run:
      
The three largest elements are: 12 9 8
      
*/

 

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