# 数组旋转的块交换算法 > 原文： [https://www.geeksforgeeks.org/block-swap-algorithm-for-array-rotation/](https://www.geeksforgeeks.org/block-swap-algorithm-for-array-rotation/) 编写一个函数`turn(ar[], d, n)`，该函数将大小为`n`的`arr[]`旋转`d`个元素。  将上面的数组旋转 2 将使数组  **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**： ## C++ ```cpp #include <bits/stdc++.h> using namespace std; /*Prototype for utility functions */ void printArray(int arr[], int size);  void swap(int arr[], int fi, int si, int d);  void leftRotate(int arr[], int d, int n)  {      /* Return If number of elements to be rotated       is zero or equal to array size */     if(d == 0 || d == n)          return;      /*If number of elements to be rotated      is exactly half of array size */     if(n - d == d)      {          swap(arr, 0, n - d, d);          return;      }      /* If A is shorter*/             if(d < n - d)      {          swap(arr, 0, n - d, d);          leftRotate(arr, d, n - d);          }      else /* If B is shorter*/             {          swap(arr, 0, d, n - d);          leftRotate(arr + n - d, 2 * d - n, d); /*This is tricky*/     }  }  /*UTILITY FUNCTIONS*/ /* function to print an array */ void printArray(int arr[], int size)  {      int i;      for(i = 0; i < size; i++)          cout << arr[i] << " ";      cout << endl;  }  /*This function swaps d elements starting at index fi  with d elements starting at index si */ void swap(int arr[], int fi, int si, int d)  {      int i, temp;      for(i = 0; i < d; i++)      {          temp = arr[fi + i];          arr[fi + i] = arr[si + i];          arr[si + i] = temp;      }  }  // Driver Code int main()  {      int arr[] = {1, 2, 3, 4, 5, 6, 7};      leftRotate(arr, 2, 7);      printArray(arr, 7);      return 0;  }  // This code is contributed by rathbhupendra ```