Find the minimum k count and k count

Find the minimum k count and k count

Find the minimum k count

1. Description

Find the minimum k number in an array with a length of n. (The maximum k number solution is similar)

2. Sorting

The idea is relatively simple. First, sort the n number, and then enter the k Number.

The time complexity of this method is relatively large. Assume that we use the fast-forward mode and require O (nlogn). Then, we need O (k) to output k numbers, which requires O (nlogn )~

Code omitted.

3. The block movement method is relatively good, and the algorithm is simple and easy to implement. First, the first k number in the array is used as the minimum candidate block. Then, this block is moved back. Each time it is moved, the current number and the maximum number in the block are compared. If it is smaller than the maximum number, it is replaced, reselect the maximum number of blocks.
As shown in:


The time complexity of this method is O (k) + O (n-k) k = O (nk ).
Another way to improve is to put the k number in a maximum heap. Every time you move an update, it is a process of updating the heap, if the current number is smaller than the top element of the heap (the maximum number in k number), we will update the heap. The update heap only requires O (logk ). Therefore, the time complexity of this improvement method is O (nlogk ).
4. Quick Selection
This method is difficult to understand, but the time complexity is O (n ).
Reference: https://github.com/julycoding/The-Art-Of-Programming-By-July/blob/master/ebook/zh/02.01.md