Implementation of Top N Problems

Problem description: Find the maximum N number in the n-length sequence.

1. Bubble Sorting

You can put the maximum number of bubbles at the end of the sequence and bubble the sequence n times.

Time Complexity: O (N * n)

Space complexity: O (1)

 

2. Scan the array and store the N largest number in the cache. When there is a larger number, replace the number in the cache.

Top_n (A, n) n = length of a create array T [N] = {-∞} t = 0 for I = 0, n-1 do if T [N-1] <A [I] Then insert a [I] To sorted array T []

Time Complexity: O (N * n)

Space complexity: O (N)

 

You can use the minimum heap instead of the maximum N number of cached array storage. In this way, when a [I] is greater than the heap top element, use a [I] instead of the heap top element, and then adjust the heap, complexity: O (N * lgn)

 

3. Heap sorting and priority queue

Construct a heap and extract n elements from the top of the heap

Time Complexity: O (N + N * lgn)

Space complexity: O (1)