Merge Sort

• 原理
  先 Divide 到 最小 再 Conquer，所以调用方式中的 Merge 在最后
  Divide 无脑二分，Conquer 合并

def merge_sort(arr):
    if len(arr) > 1:
        mid = len(arr) // 2  # Finding the mid of the array
        L = arr[:mid]  # Dividing the array elements into 2 halves
        R = arr[mid:]
 
        merge_sort(L)  # Sorting the first half
        merge_sort(R)  # Sorting the second half
 
        i = j = k = 0
 
        # Copy data to temp arrays L[] and R[]
        while i < len(L) and j < len(R):
            if L[i] < R[j]:
                arr[k] = L[i]
                i += 1
            else:
                arr[k] = R[j]
                j += 1
            k += 1
 
        # Checking if any element was left
        while i < len(L):
            arr[k] = L[i]
            i += 1
            k += 1
 
        while j < len(R):
            arr[k] = R[j]
            j += 1
            k += 1
 
    return arr

Links

SQL Join Algorithm