MaximumSumCircularSubarray.js

/*
Given a circular array C of integers represented by A, find the maximum possible sum of a non-empty subarray of C.

Here, a circular array means the end of the array connects to the beginning of the array.  (Formally, C[i] = A[i] when 0 <= i < A.length, and C[i+A.length] = C[i] when i >= 0.)

Also, a subarray may only include each element of the fixed buffer A at most once.  (Formally, for a subarray C[i], C[i+1], ..., C[j], there does not exist i <= k1, k2 <= j with k1 % A.length = k2 % A.length.)

Example 1:

Input: [1,-2,3,-2]
Output: 3
Explanation: Subarray [3] has maximum sum 3
Example 2:

Input: [5,-3,5]
Output: 10
Explanation: Subarray [5,5] has maximum sum 5 + 5 = 10
Example 3:

Input: [3,-1,2,-1]
Output: 4
Explanation: Subarray [2,-1,3] has maximum sum 2 + (-1) + 3 = 4
Example 4:

Input: [3,-2,2,-3]
Output: 3
Explanation: Subarray [3] and [3,-2,2] both have maximum sum 3
Example 5:

Input: [-2,-3,-1]
Output: -1
Explanation: Subarray [-1] has maximum sum -1
*/



var maxSubarraySumCircular = function(A) {
    
    function Kadane(A){
        let cursum = A[0]
        let maxsum = A[0]
        for(var i = 1; i<A.length; i+=1){
            cursum = Math.max(A[i],cursum+A[i])
            maxsum = Math.max(cursum,maxsum)
        }
        return maxsum
    }
    
    k = Kadane(A)
    CS = 0
    for(var i = 0 ;i<A.length;i+=1){
        CS += A[i]
        A[i] = -A[i]
    }
    CS = CS + Kadane(A)
    
    if(CS>k && CS!=0){
        return CS
    }
    else{
        return k
    }
};