Binary search in a numerical array

Question

I have a sorted array, the first value is always equal or grater than 1, and I need to find the index of the element most to the left, which is equal or greater than N.

[1, 3, 3, 4, 5, 7, 11, 11, 12, 15]

What I need is a recursive binary search function that finds the expected element, so in the example, when N is equal to 11, it returns 6 as an output.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf — Tigran Abrahamyan, Feb 12 '21 at 14:46
_"What I need is a recursive binary search function that finds the expected element"_ - Have fun implementing it (SO is not a free code writing service). If you have an actual problem with it you can come back and we will help you with that (assuming you provide a [mcve] so we can reproduce the problem). — Andreas, Feb 12 '21 at 14:46
@Andreas ```.indexOf()``` is always return the first finded index — Tigran Abrahamyan, Feb 12 '21 at 14:50
A binary search implementation is given in [this answer](https://stackoverflow.com/a/29018745/1563833) — Wyck, Feb 12 '21 at 15:05

Reflective · Answer 1 · 2021-02-12T20:49:00.617

1

EDITED!!!

Ok, now I got the question asked, my previous response was because of not reading well the question. The answer is not much complex than previous. Note: If there's no value >= n, index will be -1, otherwise you'll get the index of the first met value in your sorted array >= n.

var n = 11;
var idx = [1, 3, 3, 4, 5, 7, 11, 11, 12, 15].findIndex(each => each >= n);
console.log('idx = '+idx);

edited Feb 12 '21 at 20:49

answered Feb 12 '21 at 14:51

Reflective

3,854
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And for `N = 10`? – Andreas Feb 12 '21 at 14:54
now reading the question well , I've posted an edit which is probably the lightest solution. – Reflective Feb 12 '21 at 20:51

score 0 · Answer 2 · answered Feb 12 '21 at 14:55

0

A simple for loop will do the trick, as seen with how it is implemented in this function.

let arr=[1, 3, 3, 4, 5, 7, 11, 11, 12, 15]; // Array you want to test
let n=11; // Number to be n
function getVal(a,num){
   for(let i=0;i<a.length;++i){
      if(a[i]>=num)return i; // Look for val that's >= n.
   }
}
getVal(arr,n);

answered Feb 12 '21 at 14:55

Plantera

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How is that a binary search? And why are you reimplementing Array.findIndex – Wyck Feb 12 '21 at 15:01

Binary search in a numerical array

2 Answers2