maximum_circular_subarray.cpp

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#include <cassert>     
#include <iostream>   
#include <vector>     
 

namespace dynamic_programming {
int maxCircularSum(std::vector<int>& arr)
{
    // Edge Case
    if (arr.size() == 1)
        return arr[0];
  
    // Sum variable which stores total sum of the array.
    int sum = 0;
    for (int i = 0; i < arr.size(); i++) {
        sum += arr[i];
    }
  
    // Every variable stores first value of the array.
    int current_max = arr[0], max_so_far = arr[0], current_min = arr[0], min_so_far = arr[0];
  
    // Concept of Kadane's Algorithm
    for (int i = 1; i < arr.size(); i++) {
        // Kadane's Algorithm to find Maximum subarray sum.
        current_max = std::max(current_max + arr[i], arr[i]);
        max_so_far = std::max(max_so_far, current_max);
  
        // Kadane's Algorithm to find Minimum subarray sum.
        current_min = std::min(current_min + arr[i], arr[i]);
        min_so_far = std::min(min_so_far, current_min);
    }
  
    if (min_so_far == sum)
        return max_so_far;
  
    // Return the maximum value
    return std::max(max_so_far, sum - min_so_far);
}
}  // namespace dynamic_programming

static void test() {
    // Description of the test
    // Input: arr[] = {8, -8, 9, -9, 10, -11, 12}
    // Output: 22 
    // Explanation: Subarray 12, 8, -8, 9, -9, 10 gives the maximum sum, that is 22.
 
    std::vector<int> arr = {8, -8, 9, -9, 10, -11, 12}; 
    assert(dynamic_programming::maxCircularSum(arr) == 22); // this ensures that the algorithm works as expected
 
    arr = {8, -8, 10, -9, 10, -11, 12};
    assert(dynamic_programming::maxCircularSum(arr) == 23);
 
    std::cout << "All tests have successfully passed!\n";
}
 

int main() {
     test();  // run self-test implementations
     return 0;
}