DSA-Practice/MaximumSubArraySum.cpp at main · TheMahirK/DSA-Practice · GitHub

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/*
Program Name : Maximum Subarray sum
Program Description : Return Maximum sum possible in subarray
*/

#include <iostream>
using namespace std;

void display(vector<int> &arr)
{
    for(auto x : arr)
    {
        cout << x << ' ';
    }
    cout << endl;
}


/*
1. Algorithm Used : Brute Force
   Time Complexity : O(N^3)
   Auxiliary Space Requirement : O(1)
   Intuition : Generate all subarrays and find sum of each subarray
*/
int maxSubarraySum1(vector<int> &arr)
{
    int maxSum = INT_MIN;
    int n = arr.size();
    for(int i=0; i<n; i++)
    {
        for(int j=i; j<n; j++)
        {
            int currSum = 0;
            for(int k=i; k<=j; k++)
            {
                currSum += arr[k];
            }
            maxSum = max(currSum, maxSum);
        }
    }
    return maxSum;
}

/*
2. Algorithm Used : Better
   Time Complexity : O(N^2)
   Auxiliary Space Requirement : O(1)
   Intuition : Optimization of 1st algorithm
*/
int maxSubarraySum2(vector<int> &arr)
{
    int maxSum = INT_MIN;
    for(int i=0; i<arr.size(); i++)
    {
        int currSum = 0;
        for(int j=i; j<arr.size(); j++)
        {
            currSum += arr[j];
        if(currSum > maxSum)
        {
            maxSum = currSum;
        }
        }

    }
    return maxSum;
}


/*
2. Algorithm Used : Optimal - Kadane's Algorithm
   Time Complexity : O(N)
   Auxiliary Space Requirement : O(1)
   Intuition : Choose only positive subarray sum for considering max. sum
*/
int maxSubarraySum3(vector<int> &arr)
{
    int n = arr.size();
    int maxSum = INT_MIN;
    int currSum = 0;
    // int start = -1, end = -1;
    // int currStart = -1;
    for(int i=0; i<n; i++)
    {
        // if(currSum == 0)
        // {
        //     currStart = i;
        // }

        currSum += arr[i];
        if(currSum > maxSum)
        {
            maxSum = currSum;
            // start = currStart;
            // end = i;
        }
        if(currSum < 0)
        {
            currSum = 0;
        }
    }
    // vector<int> subArr(arr.begin()+start, arr.begin()+end+1);
    // display(subArr);
    return maxSum;
}


int main()
{

    vector<int> arr = {-2,-3,4,-1,-2,1,5,-3};
    display(arr);

    cout << maxSubarraySum3(arr) << endl;


    return 0;
}