用于数组旋转的块交换算法的 Python3 程序

编写一个函数rotate(ar[], d, n) 将大小为 n 的 arr[] 旋转 d 个元素。

将上述数组旋转 2 次将生成数组

算法 ：

Initialize A = arr[0..d-1] and B = arr[d..n-1]
1) Do following until size of A is equal to size of B

  a)  If A is shorter, divide B into Bl and Br such that Br is of same 
       length as A. Swap A and Br to change ABlBr into BrBlA. Now A
       is at its final place, so recur on pieces of B.  

   b)  If A is longer, divide A into Al and Ar such that Al is of same 
       length as B Swap Al and B to change AlArB into BArAl. Now B
       is at its final place, so recur on pieces of A.

2)  Finally when A and B are of equal size, block swap them.

递归实现：

Python3

# Wrapper over the recursive function leftRotateRec()
# It left rotates arr by d.
def leftRotate(arr, d, n):
    leftRotateRec(arr, 0, d, n);
 
def leftRotateRec(arr, i, d, n):
    '''
     * Return If number of elements to be
     rotated is zero or equal to array size
     '''
    if (d == 0 or d == n):
        return;
 
    '''
     * If number of elements to be rotated
     is exactly half of array size
     '''
    if (n - d == d):
        swap(arr, i, n - d + i, d);
        return;
 
    ''' If A is shorter '''
    if (d < n - d):
        swap(arr, i, n - d + i, d);
        leftRotateRec(arr, i, d, n - d);
        ''' If B is shorter '''
    else:
        swap(arr, i, d, n - d);
         
        ''' This is tricky '''
        leftRotateRec(arr, n - d + i, 2 * d - n, d);
 
''' UTILITY FUNCTIONS '''
''' function to print an array '''
def printArray(arr, size):
    for i in range(size):
        print(arr[i], end = " ");
    print();
 
'''
 * This function swaps d elements starting at
 * index fi with d elements starting at index si
 '''
def swap(arr, fi, si, d):
    for i in range(d):
        temp = arr[fi + i];
        arr[fi + i] = arr[si + i];
        arr[si + i] = temp;
 
# Driver Code
if __name__ == '__main__':
    arr = [1, 2, 3, 4, 5, 6, 7];
    leftRotate(arr, 2, 7);
    printArray(arr, 7);
 
# This code is contributed by Rohit_ranjan

输出：

3 5 4 6 7 1 2

迭代实现：
这是相同算法的迭代实现。此处使用相同的实用函数swap()。

时间复杂度： O(n)
有关数组旋转的其他方法，请参阅以下帖子：
https://www.geeksforgeeks.org/array-rotation/
https://www.geeksforgeeks.org/program-for-array-rotation-continued-reversal-algorithm/

有关更多详细信息，请参阅有关数组旋转的块交换算法的完整文章！