binary_search | pure Ruby binary search and index methods | Search Engine library

I was just watching an interesting CPP Con video on YouTube about sorting, and part of it addressed linear versus binary searching.

Modern CPUs do some very interesting predictive work. They may guess ahead and can be a LOT more efficient if you follow the path they think your code is going to take. Binary searches make it impossible for that to work, so they can actually be slower on modern hardware where older hardware didn't do this, and thus binary searches were typically much faster as soon as the sample size grew to something over maybe as few as 20 values.

https://www.youtube.com/watch?v=FJJTYQYB1JQ&t=2272s

So to some extent, your sample size will matter, but this talk may also shed some light.

while condition should be first <= last instead of first < last. Also, return a negative number (e.g. -1) if item is not found (because 0 means that item is found at index 0).

Here is the fixed code:

You're right to be confused by this example. With a range of 4..5, the guess (midVal) would be 4. The only way the line of code GuessNumber(lowVal, midVal-1); would be executed is if the user answered "low" which is:

1. a lie, or
2. their number is out of range.

The example code doesn't account for search values outside the initial input range, which a binary search should do.

The last paragraph explains the issue with using the absolute difference:

If you need to do as few iterations as possible, you can terminate when the interval gets small, but try to do a relative comparison of the bounds, not just an absolute one. The reason for this is that doubles can never give you more than 15 decimal digits of precision so if the search space contains large numbers (say on the order of billions), you can never get an absolute difference of less than 10-7.

The absolute difference between a and b is

This should work:

1. You are passing strcmp to bsearch. strcmp takes const char* arguments, bsearch epects a function with const void*.
2. You are passing strcmp to bsearch. It compares strings, not elements of fruit_shelf_t.
3. myStrCmp still compares strings, not fruit_shelf_t with key.
4. Do not cast the result of bsearch. Do not cast the function pointer to a different type.
5. for(int i; i < is not initializting i...
6. if(!buff){ checks if buff is not set. Should be if(buff){.

1. I see no reason to pass a pointer to a char *, just pass the key itself.
2. The callback from bsearch compares key with the element from the array.

returns the index of the first occurence of an element in a sorted array,

Your binary search algorithm requires that the data is sorted before you call it.

Example:

In your code you are not considering that mid+1 can be equal to b_size, suppose b_size=1 then mid=0 and mid+1=1, it means you are checking for a value at index 1 i.e. b[1] that is out of bound for array b.