K-way Merge helps you solve problems that involve a set of sorted arrays.
Whenever you’re given ‘K’ sorted arrays, you can use a Heap to efficiently perform a sorted traversal of all the elements of all arrays. You can push the smallest element of each array in a Min Heap to get the overall minimum. After getting the overall minimum, push the next element from the same array to the heap. Then, repeat this process to make a sorted traversal of all elements.
The pattern looks like this:
- Insert the first element of each array in a Min Heap.
- After this, take out the smallest (top) element from the heap and add it to the merged list.
- After removing the smallest element from the heap, insert the next element of the same list into the heap.
- Repeat steps 2 and 3 to populate the merged list in sorted order.
How to identify the K-way Merge pattern:
- The problem will feature sorted arrays, lists, or a matrix
- If the problem asks you to merge sorted lists, find the smallest element in a sorted list.
Problems featuring the K-way Merge pattern:
- Merge K Sorted Lists (medium)
- K Pairs with Largest Sums (Hard)