/*
* you are give a list Listy, which doesnt have method to get number of element
* you are given method GetELementAt(i) which returns value at index i
* if i is out of bound it will return -1
* Listy has positive sorted elements only.
*
* Given x, find the index at which x is placed.
*
* Runtime : O(log N) to find lenghth and then O(log N) for BS
* so overall runtime is O(log N)
*/
public int Search(Listy list, int value)
{
if (list.GetElementAt(0) == value)
{
return(0);
}
var index = 1;
while (list.GetElementAt(index) != -1 && list.GetElementAt(index) < value)
{
index = index * 2;
}
return(BinarySearch(list, index / 2, index, value));
}
private int BinarySearch(Listy list, int start, int end, int value)
{
if (start > end)
{
return(-1);
}
var mid = (start + end) / 2;
var midVal = list.GetElementAt(mid);
if (midVal == value)
{
return(mid);
}
if (midVal == -1 || value < midVal)
{
// Search left
return(BinarySearch(list, start, mid - 1, value));
}
else
{
return(BinarySearch(list, mid + 1, end, value));
}
}