/**

* Question Link: https://leetcode.com/problems/rotate-array/

* Primary idea: reverse the whole array, then reverse parts of it seperately

*

* Note: Argument of a function in Swift is let by default, so change it to var if you need to alter the value

*

* Time Complexity: O(n), Space Complexity: O(1)

*

*/

class RotateArray {

func rotate(inout nums: [Int], _ k: Int) {

var k = k % nums.count

_reverse(&nums, 0, nums.count - 1)

_reverse(&nums, 0, k - 1)

_reverse(&nums, k, nums.count - 1)

}

private func _reverse(inout nums: [Int], _ startIdx: Int, _ endIdx: Int) {

// edge case

if startIdx < 0 || endIdx > nums.count || startIdx >= endIdx {

return

}

var startIdx = startIdx

var endIdx = endIdx

while startIdx < endIdx {

_swap(&nums, startIdx, endIdx)

startIdx += 1

endIdx -= 1

}

}

private func _swap(inout nums: [Int], _ p: Int, _ q: Int) {

var temp: Int = nums[p]

nums[p] = nums[q]

nums[q] = temp

}