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MaySolDay15.swift
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MaySolDay15.swift
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//
// MaySolDay15.swift
// LeetCodeChallenge
//
// Created by Michael Ho on 5/30/20.
// Copyright © 2020 Michael Ho. All rights reserved.
//
// LeetCode: https://leetcode.com/problems/maximum-sum-circular-subarray/
class MaySolDay15 {
func maxSubarraySumCircular(_ A: [Int]) -> Int {
guard A.count > 0 else { return 0 }
if A.count == 1 {
return A[0]
}
var output = Int.min
var current = A[0]
// Single interval
for i in 1..<A.count {
current = max(A[i] + current, A[i])
output = max(output, current)
}
var right = A
for i in 1..<A.count {
let rightIdx = A.count - 1 - i
right[rightIdx] = right[rightIdx + 1] + A[rightIdx]
}
var maxRight = right
for i in 1..<A.count {
let rightIdx = A.count - 1 - i
maxRight[rightIdx] = max(maxRight[rightIdx + 1], right[rightIdx])
}
var leftSum = 0
// Double interval
for i in 0..<A.count - 2 {
leftSum += A[i]
// Note that we don't need to examine i + 1 since it is cosecurive
// that was covered in single interval
output = max(output, leftSum + maxRight[i + 2])
}
return output
}
}