Reducing process time of two map using c++ - c++

Question

I have two maps: Pkt_creatingmap and Pkt_arrivalmap. The number of elements in (Pkt_creatingmap) map is much more than the number of elements in (Pkt_arrivalmap) map [i.e.: total number of elements in Pkt_creatingmap about 650000 elements and total number of element in Pkt_arrivalmap about 72000 elements].
I want to compare the key IDs (firsts) in (Pkt_creatingmap) map and (Pkt_arrivalmap) map. If it is equal then subtract the values of key IDs (seconds) and store the result in list (TotalTrafficETED).
I write below code to do this task, However it takes a long time to accomplish (i.e.: it is time consuming). Not all elements in (Pkt_creatingmap) map are needed in this process. The process of subtraction depends only on the elements of (Pkt_arrivalmap) map.
Is there method to reduce the running time? (i.e.: can the iterator of (Pkt_creatingmap) map end at the end location of (Pkt_arrivalmap) map iterator?
Hope my question is clear.
Anyone can help me please or give me another ideal to do this task ..
#include <iostream>
#include <fstream>
#include <string>
#include <stdint.h>
#include <sstream>
#include <cmath>
#include <map>
#include <iterator>
#include <list>
using namespace std;
int main()
{
map<double_t, double_t> Pkt_arrivalmap;
map<double_t, double_t> Pkt_creatingmap;
list<double_t> TotalTrafficETED;
int pos, pos2, pos3;
double_t ArrivingID, CreatingID, ArrivingTime, CreatingTime, Pkt_ETED, TTETED;
string line, search, word1 = "ns", word2 = "Pkt_create", word3 = "Pkt_recv";
ifstream inf;
inf.open("123.txt");
if (inf.is_open()) {
while (getline(inf, line)) {
if (line.find("Pkt_recv") != string::npos) {
pos = line.find(word1);
pos3 = line.find(word3);
line.replace(pos, word1.length(), " "); // to remove "ns"
line.replace(pos3, word3.length(), " "); // to remove "Pkt_recv"
istringstream iss(line);
double_t column1;
//double_t column3;
double_t column2;
iss >> column1 >> column2;
//cout << column1 <<" "<< column2 <<" "<< " "<< endl;
Pkt_arrivalmap[column1] = column2;
}
}
inf.close();
}
else
cout << "Unable to open file inf \n";
for (std::map<double_t, double_t>::iterator it = Pkt_arrivalmap.begin(); it != Pkt_arrivalmap.end(); it++) {
cout << "Arrival info."
<< " " << it->first << " " << it->second << " " << Pkt_arrivalmap.size() << endl;
}
inf.open("123.txt");
if (inf.is_open()) {
while (getline(inf, line)) {
if (line.find("Pkt_create") != string::npos) {
pos = line.find(word1);
pos2 = line.find(word2);
line.replace(pos, word1.length(), " "); // to remove "ns"
line.replace(pos2, word2.length(), " "); // to remove "Pkt_create"
istringstream iss(line);
double_t column1;
//double_t column3;
double_t column2;
iss >> column1 >> column2;
//cout << column1 <<" "<< column2 <<" "<< " "<< endl;
Pkt_creatingmap[column1] = column2;
}
}
inf.close();
}
else
cout << "Unable to open file inf \n";
for (std::map<double_t, double_t>::iterator it = Pkt_creatingmap.begin(); it != Pkt_creatingmap.end(); it++) {
cout << "Creating info."
<< " " << it->first << " " << it->second << " " << Pkt_creatingmap.size() << endl;
}
for (std::map<double_t, double_t>::iterator it = Pkt_arrivalmap.begin(); it != Pkt_arrivalmap.end(); it++) {
ArrivingID = it->first;
ArrivingTime = it->second;
//cout << "Ahmed" <<" "<< ArrivingID <<endl;
for (std::map<double_t, double_t>::iterator it = Pkt_creatingmap.begin(); it != Pkt_creatingmap.end(); it++) {
CreatingID = it->first;
CreatingTime = it->second;
if (ArrivingID == CreatingID) {
Pkt_ETED = (ArrivingTime - CreatingTime) / 1000000000;
TotalTrafficETED.push_back(Pkt_ETED);
Pkt_creatingmap.erase(it->first);
Pkt_arrivalmap.erase(it->first);
cout << "Pkt_ID:" << CreatingID << ","
<< "Pkt_ETED:" << Pkt_ETED << endl;
}
}
}
for (std::list<double_t>::iterator it = TotalTrafficETED.begin(); it != TotalTrafficETED.end(); it++) {
TTETED += *it / TotalTrafficETED.size();
}
cout << "Total Traffic ETED"
<< " " << TTETED << endl;
return 0;
}

Answer 1

If you want to find an element with a given ID in a map, the method map::find is very efficient and proceeds logarithmic in size of the map, because it is a sorted container. In your code, you do two for loop and the complexity is quadratic. Thus, you have to write something like that :
for (std::map<double_t,double_t>::iterator it = Pkt_arrivalmap.begin(); it != Pkt_arrivalmap.end(); it++)
{
ArrivingID =it->first;
ArrivingTime=it->second;
//cout << "Ahmed" <<" "<< ArrivingID <<endl;
map<double_t,double_t>::iterator it2 = Pkt_creatingmap.find(ArrivingID);
if (it2!=Pkt_creatingmap.end()){ // Found equivalent key
CreatingTime=it2->second;
Pkt_ETED=(ArrivingTime-CreatingTime)/1000000000;
TotalTrafficETED.push_back(Pkt_ETED);
Pkt_creatingmap.erase(it->first);
Pkt_arrivalmap.erase(it2->first);
cout <<"Pkt_ID:"<<CreatingID<<","<<"Pkt_ETED:"<<Pkt_ETED<<endl;
}
}