Xavier Chretien

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# Day 2: Fixed point

• Difficulty: Easy
• Programming language: Kotlin

## Problem

A fixed point in an array is an element whose value is equal to its index.
Given a sorted array of distinct elements, return a fixed point, if one exists. Otherwise, return `false`.

For example:

• Given `[-6, 0, 2, 40]`, you should return `2`
• Given `[1, 5, 7, 8]`, you should return `false`

## My solution

This is an easy one and I don't want to go to a very complex solution. Let's just iterate the array and find the fixed point ๐

``````/**
* Find each fixed point in a sorted array.
*
* @param array, sorted array
* @return an list with each fixed points, the list is empty if there is no fixed points.
*/
fun findFixedPoint(array: IntArray): List<Int>{
if(array[1] < array[0]) throw IllegalArgumentException("Array not sorted")

val pointFixedFound = mutableListOf<Int>()
for ((index, value) in array.withIndex()) {
if(index == value){
}
}

return pointFixedFound.toList()
}
``````

## UPDATED VERSION

As

suggests in the comments, I didn't really follow the question asked. The question is to return A fixed point not all fixed points, so there is the updated version (thanks again to Nick Holmes).

``````fun findFixedPoint(array: IntArray): Int? {
val pointFixedFound = mutableListOf<Int>()

for ((index, value) in array.withIndex()) {
if(index == value){
return index
} else if (value > index) {
break
}
}
return null
}
``````

The function returns null if there is no fixed point because I didn't find if this is possible to return an int or false in Kotlin, so I return null instead.

Nick Holmes

As a constructive critique of your solution:

A)

``````if(array[1] < array[0]) throw IllegalArgumentException("Array not sorted")
``````

You are claiming the array is not sorted if the first two elements are not sorted. What about the array [1, 3, 2] or [1, 1, 2]? Also, what if the array is of length 0 or 1?

You weren't asked to validate that the array was sorted, so you could simply remove this line.

B)

``````return pointFixedFound.toList()
``````

You are asked to return either an integer or a false, but you are returning a list. Although your list contains the answer, if this was an interview question, I would mark you down on this - demonstrating the ability to extract all detail out of a provided specification is important.

C)
Finally, given that this is coding challenge, and that we are told that input list is sorted and distinct, I think a "more optimal" solution is evident;

• as soon as you find a cell value equal to the index, just return the value - no need to go to the end of the list.

• as soon as you find a cell value greater than the index, just return false - there can be no fixed points from here on.

Xavier Chretien

First, thank you for your critique! ๐

A) About the first line, you are right I could simply remove that line.

B) In an interview, I would probably follow the problem asked without any modification. In that case, I choose to return every fixed point on the given array but you are right I should just respect the problem.

C) I will update the post with your proposition

Once again thank you I really appreciate your comment ๐