C program for merge sort without recursion

Save Article. Like Article. Recursive Python Program for merge sort. First merge subarrays of. First merge subarrays. Iterative Merge sort Bottom Up. Increasing sub array size by powers of 2. Now, you have nothing but groups of 4 plus a possible remainder. Using a loop around the previous logic, do it all again except this time work in groups of 4. This loop runs until there is only one group.

Quoting from Algorithmist :. Bottom-up merge sort is a non-recursive variant of the merge sort, in which the array is sorted by a sequence of passes. During each pass, the array is divided into blocks of size m.

Every two adjacent blocks are merged as in normal merge sort , and the next pass is made with a twice larger value of m. Both recursive and non-recursive merge sort have same time complexity of O nlog n. This is because both the approaches use stack in one or the other manner. The main reason you would want to use a non-recursive MergeSort is to avoid recursion stack overflow. However, in the recursive version of MergeSort, the million element sort results in million recursive calls to the MergeSort.

At a few hundred bytes per stack recursion, this overflows the recursion stack even though the process easily fits within heap memory. Doing the Merge sort using dynamically allocated memory on the heap-- I am using the code provided by Rama Hoetzlein above, but I am using dynamically allocated memory on the heap instead of using the stack-- I can sort my million records with the non-recursive merge sort and I don't overflow the stack.

An appropriate conversation for website "Stack Overflow"! PPS: gigabytes on the heap?!! Well, it's a virtual heap on a Hadoop cluster, and the MergeSort will be implemented in parallel on several machines sharing the load I am new here. I have modified Rama Hoetzlein solution thanks for the ideas.

My merge sort does not use the last copy back loop. Plus it falls back on insertion sort. I have benchmarked it on my laptop and it is the fastest. Even better than the recursive version. By the way it is in java and sorts from descending order to ascending order.

And of course it is iterative. It can be made multithreaded. The code has become complex. So if anyone interested, please have a look.

Just in case anyone's still lurking in this thread I've adapted Rama Hoetzlein's non-recursive merge sort algorithm above to sort double linked lists. Problem : : The following C program, using recursion, performs quick sort. Notify of. Inline Feedbacks. Iconic One Theme Powered by Wordpress. Would love your thoughts, please comment. When the solution to each subproblem is ready, we 'combine' the results from the subproblems to solve the main problem.

Suppose we had to sort an array A. A subproblem would be to sort a sub-section of this array starting at index p and ending at index r , denoted as A[p.. If q is the half-way point between p and r, then we can split the subarray A[p.. In the conquer step, we try to sort both the subarrays A[p.. If we haven't yet reached the base case, we again divide both these subarrays and try to sort them.

When the conquer step reaches the base step and we get two sorted subarrays A[p.. The MergeSort function repeatedly divides the array into two halves until we reach a stage where we try to perform MergeSort on a subarray of size 1 i. After that, the merge function comes into play and combines the sorted arrays into larger arrays until the whole array is merged. As shown in the image below, the merge sort algorithm recursively divides the array into halves until we reach the base case of array with 1 element.

After that, the merge function picks up the sorted sub-arrays and merges them to gradually sort the entire array. Every recursive algorithm is dependent on a base case and the ability to combine the results from base cases. Merge sort is no different.