CODEWITHSUNDEEP
algorithmsearchtime-complexitypseudocode
Navidk
Navidk

Reputation: 642

Recursive and Iterative Binary Search: Which one is more efficient and why?

I have written the algorithms for recursive and iterative binary search:

Recursive

AlgorithmBinSrch(a, i,l,x)
// Given an array a[i :l] of elementsin nondecreasing
// order,1<i <=l,determinewhetherx is present,and
// if so,return j suchthat x = a[j];elsereturn 0.
{
    if (l =i) // If Small(P) {
        if(x=a[i]) 
            return i;
        else 
            return 0;
    } else { // ReduceP into a smallersubproblem.
        mid:=[(i+l)/2]; 
        if (x = a[mid]) 
            return mid;
        else if (x <a[mid]) 
            returnBinSrch(a,i,mid-1,x);
        else
            returnBinSrch(a,mid1+,l,x);
    } 
}

Iterative

// Given an array a[1:n] of elementsin nondecreasing
// order,n >=0,determine whether x is present,and
// if so,return j suchthat x = a[j];elsereturn 0.
{
    low :=1;high :=n;
    while (low<=high) {
        mid:= [(low+high)/2];
        if (x <a[mid])
            high :=mid-1;
        else if (x >a[mid])
            low :=mid+ 1;
        else 
            return mid;
    } 
    return 0;
}

Which one of them will be more efficient and how does one find that. Should count statements be added to count number of steps in each and based on that can efficiency be determined?

Upvotes: 14

Views: 15626

Answers (2)

Peter
Peter

Reputation: 2927

With regard to time complexity, recursive and iterative methods both will give you O(log n) time complexity, with regard to input size, provided you implement correct binary search logic.

Focusing on space complexity, the iterative approach is more efficient since we are allocating a constant amount O(1) of space for the function call and constant space for variable allocations, while the recursive approach takes O(log n) space.

Upvotes: 24

Avishek Bhattacharya
Avishek Bhattacharya

Reputation: 6994

There is no different w.r.t Big O analysis between these two versions. Both will run O(logn) if written correctly.
There have been concerns around the recursive program regarding the function stack it is going to use. However, once you see it carefully, the recursive version is a tail recursion. Most of the modern compiler converts the tail recursion into iterative program. Thus, there won't be any issue regarding the usage of the function stack.
Hence, both will run with same efficiency.

Personally, I like the recursive code. It is elegant, easy and maintainable. Binary search is a notoriously difficult algorithm to implement correctly. Even, java library had bug in the implementation.

Upvotes: 9

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