C#•2y ago

✅ Why is my code still wrong?

So I am resolving this LC puzzle https://leetcode.com/problems/binary-search/description/ I think my code is almost there, it still comes with a couple of failed test cases like this (see the attached screenshot). Could anyone kindly point me in the right direction?

public static class Extensions{
    public static int indexFinder<T>(this T[] nums, T target){
        return Array.FindIndex(nums, val => val.Equals(target));
    }
}

public class Solution {
    
    public int Search(int[] nums, int target) {
        if(nums.indexFinder(target) == -1){
            return -1;
        } else {
                int index = nums.indexFinder(target);
                if(nums.indexFinder(target) != 1){
                   return index;
                }
            
        }
        return -1;
    }
}

public static class Extensions{
    public static int indexFinder<T>(this T[] nums, T target){
        return Array.FindIndex(nums, val => val.Equals(target));
    }
}

public class Solution {
    
    public int Search(int[] nums, int target) {
        if(nums.indexFinder(target) == -1){
            return -1;
        } else {
                int index = nums.indexFinder(target);
                if(nums.indexFinder(target) != 1){
                   return index;
                }
            
        }
        return -1;
    }
}

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10 Replies

Aaron•2y ago

why are you using FindIndex when it asks for binary search but to actually answer the question, the cause is the second if statement, the one inside the else block @morry329

Henkypenky•2y ago

also why are u using FindIndex, that is O(n) you can solve this exercise with 1 line with Array.IndexOf but it's still O(n) the challenge is to make it better

public class Solution {
    
    public int Search(int[] nums, int target)
    {
        return Array.IndexOf(nums, target);
    }
}

public class Solution {
    
    public int Search(int[] nums, int target)
    {
        return Array.IndexOf(nums, target);
    }
}

1 line a good way to approach this is to use the fact that the array is sorted to your advantage so slice it check that index vs the target and see where to go left or right sorry didn't see this line

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

morry329#OP•2y ago

Ahhh thank you so much for your insights people! I am a stupid beginner one so I did not understand how FindIndex works. So this FindIndex was not necessary as the array has been already sorted for me, right?

gush3l•2y ago

that's not binary search what you did there

Henkypenky•2y ago

it's okay, what we meant is that using FindIndex or IndexOf is not a proper solution because they are O(n), and the task required O (log n). since you are provided a sorted array you should take advantage of that in this case, specifically with binary search which only works on sorted arrays and happens to be an algorithm at O (log

are built in methods for binary search you can check the Array class but there is no fun in doing that, and it won't hold at an interview you have 2 ways to handle this 1. you can check Array.BinarySearch method source code and try to understand it or 2. check something like geekforgeeks https://www.geeksforgeeks.org/binary-search/ https://github.com/dotnet/runtime/blob/main/src/libraries/System.Private.CoreLib/src/System/Array.cs

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

morry329#OP•2y ago

Thank you so much for the links -- one more question with regards to the time complexity. So the binary search on geeksforgeeks is at O (log n) as the algorithm divides the working area in half with each iteration (like the use of middle index)?

Henkypenky•2y ago

yes, you are taking chunks, taking advantage of the sorted array you never traverse the array completely so it's better than linear

morry329#OP•2y ago

Ahhh I got it 🙂 Thank you so much for explaining that to me

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✅ Why is my code still wrong?