Question

I am using xcode

Use the following ideas to develop a nonrecursive, linear-time algorithm for the maximum-subarray problem. Start at the left end of the array, and progress toward the right, keeping track of the maximum subarray seen so far. Knowing a maximum subarray of A[1..j], extend the answer to find a maximum subarray ending at index j + 1 by using the following observation: a maximum subarray of A[1..j + 1] is either a maximum subarray of A[1..j] or a subarray A[i..j + 1], for some 1 ≤ i ≤ j + 1. Determine a maximum subarray of the form A[i..j + 1] in constant time based on knowing a maximum subarray ending at index j.

Your program is to be written in C++. Please name your file: linear_max_subarray.cpp. You’re program needs to do the following:

Receive the name of an input text file via a command line argument.

Open the given file and read all of the values into a std::vector of longs. An example input file is given below.

Finally, your program should calculate the maximum subarray for the provided data and output the value to stdout (e.g., using cout).

Notes:
- Your program should compile with the following command: g++ -std=c++11 -Wall -o linear_max_subarray linear_max_subarray.cpp.
- Your program should run correctly with the following command: ./linear_max_subarray inputs.txt.
- Your program will be tested against one file of all positive numbers, one file of all negative numers, and two files with randomly generated numbers.
- It is important the only output from your program be the number representing the maximum subarray value. Do not output extra text in the version that you submit.

Your completed program should be uploaded to Gradescope. You should receive fairly immediate feedback.

Example input file contents:

-4
6
3
7
-10
3
4
4
-8
-1


Example showing how to read command-line inputs:

// This is a simple example showing how you can read
// arguments from the command line.
//
// You can run the program as follows:
//  ./ one two three
//
// And you will get the following output:
//  Argument 0 is: ./
//  Argument 1 is: one//  Argument 2 is: two
//  Argument 3 is: three
//
// In your programming assignment, your program should
// read the second input (argv[1]) and treat it as the
// name of the file that it will read.

#include 
using std::cout;
using std::endl;

int main(int argc, char const *argv[])
{
    // An example showing how to read command line arguments
    for (auto i = 0ul; i < argc; ++i) {
        cout << "Argument " << i << " is: " << argv[i] << endl;
    }
    return 0;
}

Answer 1

#include <iostream>
#include <fstream>
#include <vector>
#include <limits.h>

using namespace std;

int* maxSubArray(vector<long> &v, int size)
{
static int maxindex[2];
int maxSumTillNow = INT_MIN;

int currentStartIndex = 0;
int currentSum = 0;

for (int i = 0; i < size; i++)
{
    currentSum = currentSum + v[i];

   if(currentSum > maxSumTillNow)
   {
    maxSumTillNow = currentSum;
    maxindex[0] = currentStartIndex;
    maxindex[1] = i;
   }

   if(currentSum<0)
   {
    currentSum = 0;
    currentStartIndex = i + 1;
   }
}

return maxindex;
}


/* Driver program to test maxSubArray */
int main(int argc, char const *argv[])
{
   if(argc <2)
      cout << "Invalid input arguments\n";

   int data;
   vector<long> v;

   ifstream myfile;
   myfile.open (argv[1]);

   while(myfile >> data)
   {
      v.push_back(data);

   }

   myfile.close();

   int *result = maxSubArray(v, v.size());

   cout << "Largest sum subarray: ";
   for (int i = result[0]; i <= result[1]; ++i)
   {
      cout << v[i] << " ";
   }

   cout << endl;

   return 0;
}

/*
input.txt

-4
6
3
7
-10
3
4
4
-8
-1

output:

Largest sum subarray: 6 3 7 -10 3 4 4

*/