Merge_sort

The meaning and use of merging and sorting

• Let's say that the current list is divided into two sections , How to collectively call it a sequence table
  

def merge(li, low, mid, high):
    i = low
    j = mid + 1
    ltmp = []
    while i<=mid and i<=high:   # As long as there are numbers on the left and right 
        if li[i] < li[j]:
            ltmp.append(li[i])
            i += 1
        else:
            ltmp.append(li[j])
            j += 1
        #while After execution , There must be a few left 
    while i <= mid:
        ltmp.append(li[i])
        i += 1
    while j <= high:
        ltmp.append(li[j])
        j += 1
    li[low:high+1] = ltmp

li = [2,4,5,7,1,3,6,8]
merge(li, 0, 3, 7)
print(li)

How to use merge

• decompose ： The smaller the list, the smaller , Until it's divided into elements
• Termination conditions ： An element is ordered
• Merge ： Merge two sequential tables , The list is getting bigger
• The time complexity is O(logn), The space complexity is O(n)
  

def merge_sort(li, low, high):
    if low < high:
        mid = (low + high) //2
        merge_sort(li, low, mid)
        merge_sort(li, mid+1, high)
        merge(li, low, mid, high)

li = list(range(100))
import random
random.shuffle(li)
print(li)
merge_sort(li, 0, len(li)-1)
print(li)

A small summary of various sorts