基于最大值索引 C++ 从 2 个向量中提取值

Question

I'm a newbie programmer trying to get used to work with vectors. In the following code I was able to find the max value of vector "V" and return it to main. Instead of that I need to return the value from the other vector corresponding to the max value index. In this case for vector "V" max value is 65.25, I want the function to return 0.05 from vector "freq" (same index). These values come from previous calculations using matrixes, adding the results to the vector with the push_back method, I just need to extract the 0.05 for further operations. Help is very well appreciated.

#include <iostream>
#include <vector>
#include <cmath>
#include <cfloat>

using namespace std;
double maxAt(vector<double> &Lvec); // MaxL value func prototype


int main() {

    vector <double> freq = {0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07};
    vector <double> V ={0, 0, 0, 0, 65.25, 0,6};
    double MaxV = maxAt(V);
    cout << MaxV << endl;
    return 0;
}



double maxAt(vector<double> &V) {
    double Lmax = DBL_MIN;
    for (auto val : V) {
         if (Lmax < val) Lmax = val;
    } 
    return Lmax;
}

Answer 1

There is no need to invent your own function that searches the maximum. You can use standard features.

Here you are.

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

int main() 
{
    std::vector<double> freq = { 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07 };
    std::vector<double> V = { 0, 0, 0, 0, 65.25, 0,6 };

    auto it = std::max_element( std::begin( V ), std::end( V ) );

    std::cout << *it << " -> " 
              << *std::next( std::begin( freq ), std::distance( std::begin( V  ), it ) )
              << '\n';

    return 0;
}

The program output is

65.25 -> 0.05

If to use your function then you should change it the following way as it is shown in the demonstrative program below.

#include <iostream>
#include <vector>

auto maxAt( const std::vector<double> &V ) 
{
    std::vector<double>::size_type max = 0;

    for ( std::vector<double>::size_type i = 1; i < v.size(); i++  ) 
    {
         if ( V[max] < V[i] ) max = i;
    } 

    return max;
}

int main() 
{
    std::vector<double> freq = { 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07 };
    std::vector<double> V = { 0, 0, 0, 0, 65.25, 0,6 };

    auto pos = maxAt( V );

    std::cout << V[pos] << " -> " 
              << *freq[pos]
              << '\n';

    return 0;
}

The program output is the same as shown above

65.25 -> 0.05

Answer 2

You could do:

double maxAt(vector<double> &V, vector<double> &freq) {
    double Lmax = DBL_MIN;
    double Lfreq = DBL_MIN;
    for (size_t i = 0; i < V.size(); ++i) {
         if (Lmax < V[i]) {
             Lmax = V[i];
             Lfreq = freq[i];
         }
    } 
    return Lfreq;
}

Also, see here for an answer that uses standard algorithms: Finding the position of the max element