Computing an inner product of tuples represented as maps : map « map multimap « C++ Tutorial

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23.1.9.Computing an inner product of tuples represented as maps

#include <map>

#include <iostream>

using namespace std;



int main()

{

  const long N = 600000; // Length of tuples x and y

  const long S = 10;     // Sparseness factor



  map<long, double> x, y;

  for (long k = 0; 3 * k * S < N; ++k)

    x[3 * k * S] = 1.0;

  for (long k = 0; 5 * k * S < N; ++k)

    y[5 * k * S] = 1.0;



  double sum;

  map<long, double>::iterator ix, iy;



  for (sum = 0.0, ix = x.begin(); ix != x.end(); ++ix) {

    long i = ix->first;

    iy = y.find(i);

    if (iy != y.end())

      sum += ix->second * iy->second;

  }

  cout << sum << endl;

  return 0;

}

23.1.map
	23.1.1.	Demonstrating an STL map
	23.1.2.	Use string as the key and value in a map
	23.1.3.	Define string-string map and loop through the value key-pair
	23.1.4.	Declare a char int map
	23.1.5.	Create string float map
	23.1.6.	Multiple map
	23.1.7.	Store objects in a map
	23.1.8.	A phone list in which a person's name is the key and the phone number is the value.
	23.1.9.	Computing an inner product of tuples represented as maps

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