Get index of number if it was inserted into a sorted array

Question

function getIndexToIns(arr, num) {
  arr.sort(function(a, b) {
    return a - b;
  });
  
  for (var i = 0; i < arr.length; i++) { // cycles through the array
    if (arr[i] >= num) { // if array value is bigger than num 
      return i; // return index pos of num bigger than value
    }
    else if (arr[i] === undefined) { // if not found 
      arr.push(num); // push to array 
      return arr.indexOf(num); // return index pos of new num <-- should return 3 in this case
    }
  }
}

console.log(getIndexToIns([2, 5, 10], 15)); // Should return 3

The mission of this is to sort an array, and return the index value of arg2 if it were in the array.

Example: getIndexToIns([10, 20, 30, 40, 50], 35) should return 3.

What I’m having trouble with, is if arg2 is not found in the array, to push it into it and return its index value. I can’t seem to make it work.

Answer 1

Another way to do it:

function getIndex(arr, num) {
  return arr.concat(num).sort(function(a, b) {
    return a - b;
  }).indexOf(num);
}

Sure there a few ways to do this but the fix in your code is below:

Working Example

function getIndexToIns(arr, num) {
  arr.sort(function(a,b) {
    return a-b;
  });
  for (var i=0;i<arr.length;i++) { // cycles through the array
    if (arr[i] >= num) { // if array value is bigger than num 
        return i; // return index pos of num bigger than value
    }
    if (i === arr.length - 1) { // if not found 
        arr.push(num); // push to array 
        return arr.indexOf(num); // return index pos of new num <-- should return 3 in this case
    }
  }
}

in your code you checked to see if (arr[i] === undefined) that will never happen, so instead check to see if you are at the end of the array, and if so, that means you haven't found your number, and then you can push it and get the index.

Answer 2

Why don't you use the .push and .indexOf methods on the array?

function arrSort(a, b) {
    return a - b;
}

function getIndexToIns(arr, num) {
    // you sort the array
    arr.sort(arrSort);

    // if it doesn't contain the num
    if(arr.indexOf(num) == -1) {
        // add the num to the array
        arr.push(num);

        // sort the array again
        arr.sort(arrSort);

        // return the index of the num
        return arr.indexOf(num);
    }

    // if the num is in the array, return its position
    return arr.indexOf(num);
}

Answer 3

Since your arrays seem already sorted, you should just use a dichotomic search to find the index, and then insert it with splice.

function getIndexToIns(arr, num) {
  var index = (function search(from, to) {
    if(from == to) return to;
    var m = Math.floor((from+to)/2);
    if(arr[m] > num) return search(from, m);
    if(arr[m] < num) return search(m+1, to);
    return m;
  })(0, arr.length);
  arr.splice(index, 0, num);
  return index;
}

Or, since it will be linear anyways, loop backwards manually:

function getIndexToIns(arr, num) {
  for(var i=arr.length; i>0 && arr[i-1]>num; --i) arr[i] = arr[i-1];
  arr[i] = num;
  return i;
}

Answer 4

You could just push num into the array then sort it out with map or sort.

function getIndexToIns(arr, num) {
  arr.push(num);
  arr.map(function(a,b) {
    a-b;
     arr.indexOf(num);
  });
  console.log(arr+'\n');
  console.log(num +' is at '+arr.indexOf(num)+'\n');
}

getIndexToIns([2, 5, 10], 15);