This gist contains few recursion programs

RecursionPrograms.swift

func binarySearchWithRecursion(arr: [Int], target: Int, s: Int, e: Int) -> Int {
    if s > e {
        return -1
    }
    
    if arr[s] == target {
        return s
    }
    
    let med = e / arr.count
    
    if target < arr[med] {
        return binarySearchWithRecursion(arr: arr, target: target, s: s, e: med - 1) 
    }
    
    return binarySearchWithRecursion(arr: arr, target: target, s: med + 1, e: e) 
}


print(binarySearchWithRecursion(arr: [1,4,6,7,8], target: 6, s: 0, e: 5))


func linearSearchWithRecursion(arr: [Int], target: Int, currentIndex: Int = 0) -> Int {
    if currentIndex == arr.count - 1 {
        return -1
    }

    if arr[currentIndex] == target {
        return currentIndex
    }
    
    return linearSearchWithRecursion(arr: arr, target: target, currentIndex: currentIndex + 1)
}


print(linearSearchWithRecursion(arr: [1,4,5,25,6,34,4], target: 55))



func checkIfArrayIsSorted(arr: [Int], currentIndex: Int = 0) -> Bool {
    if currentIndex == arr.count - 1 {
        return true
    }
    
    if arr[currentIndex] > arr[currentIndex + 1] {
        return false
    }
    
    return checkIfArrayIsSorted(arr: arr, currentIndex: currentIndex + 1)
}


print(checkIfArrayIsSorted(arr: [1,3,4,7,2]))


func countDigits(num: Int) -> Int {
    if num == 0 {
        return 0
    }
    
    return 1 + countDigits(num: num / 10)
}


print(countDigits(num: 2314))


func countZero(num: Int, count: Int) -> Int {
    if num == 0 {
        return count 
    }
    
    if num % 10 == 0 {
        return countZero(num: num / 10, count: count + 1)
    }
    
    return countZero(num: num / 10, count: count)
}


print(countZero(num: 1000200, count: 0))


func productOfDigits(num: Int) -> Int {
    if num == 0 {
        return 1
    }
    
    return num % 10 * productOfDigits(num: num / 10)
}


print(productOfDigits(num: 1223))



func sumOfDigits(num: Int) -> Int {
    if num == 0 {
        return 0
    }
    
    return num % 10 + sumOfDigits(num: num / 10)
}

print(sumOfDigits(num: 123))