RotateArray

RotateArray.swift

//Given an array, rotate the array to the right by k steps, where k is non-negative.

// Input: nums = [1,2,3,4,5,6,7], k = 3
// Output: [5,6,7,1,2,3,4]
// Explanation:
// rotate 1 steps to the right: [7,1,2,3,4,5,6]
// rotate 2 steps to the right: [6,7,1,2,3,4,5]
// rotate 3 steps to the right: [5,6,7,1,2,3,4]

//SOLUTION: 
// Reverse array, find the split point and reverse two separate arrays from left and right side.

func rotate(_ nums: inout [Int], _ k: Int) {
    
  // Exctact the length of array from steps count.
  // It's unnecessary to rotate array by steps that equal the array length, because we'll get the same array. 
    let splitPoint = k % nums.count
    
    nums.reverse()
    reverse(&nums, start: 0, end: splitPoint - 1)
    reverse(&nums, start: splitPoint, end: nums.count - 1)
    
}

func reverse(_ nums: inout [Int], start: Int, end: Int) {
   
    var s = start
    var e = end
    
        while s < e {
            var temp = nums[s]
            nums[s] = nums[e]
            nums[e] = temp
            s += 1
            e -= 1
        }
    }