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May Leetcode Challenge - Day 15

Maximum Sum Circular Subarray

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

Note:

  • -30000 <= A[i] <= 30000
  • 1 <= A.length <= 30000

Solution

https://leetcode.com/problems/maximum-sum-circular-subarray/discuss/178422/One-Pass

class Solution {
    func maxSubarraySumCircular(_ A: [Int]) -> Int {
        var total = 0
        var maxSum = -30000, curMax = 0
        var minSum = 30000, curMin = 0
        
        for a in A {
            curMax = max(curMax + a, a)
            maxSum = max(maxSum, curMax)
            curMin = min(curMin + a, a)
            minSum = min(minSum, curMin)
            total += a
        }
        
        return maxSum > 0 ? max(maxSum, total - minSum) : maxSum
    }
}

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