C++ rotate用法及代码示例

该函数在头文件<algorithm>中定义。它以[first，last]范围内的元素顺序旋转，以这种方式使得由Middle指向的元素成为新的第一个元素。
函数模板：

void rotate(ForwardIterator first, ForwardIterator middle, ForwardIterator last)
first, last: Forward Iterators to the initial and final positions of the sequence to be rotated
middle: Forward Iterator pointing to the element within the range [first, last] that is moved to the first position in the range.

Types of Rotations

1. 左旋：要向左旋转，我们需要添加矢量索引。例如，您必须将向量向左旋转3次。向量的第三个索引成为第一个元素。 vec.begin() + 3将向量向左旋转3次。
2. 右旋：要向右旋转，我们需要减去向量索引。例如，您必须将向量右旋转3次。向量的最后3个索引成为第一个元素。 vec.begin() + vec.size()-3将向量向右旋转3次。

例子：

Input:1 2 3 4 5 6 7 8 9
Output:
Old vector:1 2 3 4 5 6 7 8 9
New vector:4 5 6 7 8 9 1 2 3 // Rotated at 3th position, starting index as 0.

Input:8 2 4 6 11 0 15 8
Output:
Old vector:8 2 4 6 11 0 15 8
New vector:0 15 8 8 2 4 6 11 //Rotated at 5th position, starting index as 0.

// CPP program to rotate vector 
// using std::rotate algorithm 
  
#include<bits/stdc++.h> 
  
int main () { 
    std::vector<int> vec1{1,2,3,4,5,6,7,8,9}; 
  
    // Print old vector 
    std::cout << "Old vector:"; 
    for(int i=0; i < vec1.size(); i++) 
        std::cout << " " << vec1[i]; 
    std::cout << "\n"; 
    // Rotate vector left 3 times. 
    int rotL=3; 
  
    // std::rotate function 
    std::rotate(vec1.begin(), vec1.begin()+rotL, vec1.end()); 
  
    // Print new vector 
    std::cout << "New vector after left rotation:"; 
    for (int i=0; i < vec1.size(); i++) 
        std::cout<<" "<<vec1[i]; 
    std::cout << "\n\n"; 
  
    std::vector <int> vec2{1,2,3,4,5,6,7,8,9}; 
  
    // Print old vector 
    std::cout << "Old vector:"; 
    for (int i=0; i < vec2.size(); i++) 
        std::cout << " " << vec2[i]; 
    std::cout << "\n"; 
  
    // Rotate vector right 4 times. 
    int rotR = 4; 
  
    // std::rotate function 
    std::rotate(vec2.begin(), vec2.begin()+vec2.size()-rotR, vec2.end()); 
  
    // Print new vector 
    std::cout << "New vector after right rotation:"; 
    for (int i=0; i < vec2.size(); i++) 
        std::cout << " " << vec2[i]; 
    std::cout << "\n"; 
  
return 0; 
}

输出：

Old vector:1 2 3 4 5 6 7 8 9
New vector after left rotation:4 5 6 7 8 9 1 2 3

Old vector:1 2 3 4 5 6 7 8 9
New vector after right rotation:6 7 8 9 1 2 3 4 5

时间复杂度：Theta(n)，其中n是给定范围内的元素数。