LeetCode 189 Rotate Array (rotating Array)

LeetCode 189 Rotate Array (rotating Array)
Translation

Rotate an array with n elements to the right in K steps. For example, given n = 7 and k = 3, the array [, 7] is rotated to [, 4]. Annotation: Try multiple solutions as much as possible. There are at least three different solutions here.

Original

Rotate an array of n elements to the right by k steps.For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].Note:Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.

Analysis

Method 1

The first method I think of is to set another vector, add the elements one by one, and assign the vector to nums. You can add k elements on the right and n-k elements on the left.

The Code is as follows:

void rotate(vector
  
    &nums, int k) {    if (nums.size() == 1) return;    if (k > nums.size())  k %= nums.size();    vector
   
     newNums;    for (int i = nums.size() - k; i < nums.size(); ++i)        newNums.push_back(nums[i]);    for (int i = 0; i < nums.size() - k; ++i)        newNums.push_back(nums[i]);    nums = newNums;}Runtime: 28 ms
   
  

Timeout Method

There is another simplest method, but it timed out ......

void rotate(vector
  
    &nums, int k) {    if (nums.size() <= 1) return;    if (k > nums.size()) k %= nums.size();    while (k > 0) {        int temp = nums[nums.size() - 1];        for (int i = nums.size() -1; i >0; --i) {            nums[i] = nums[i - 1];        }        nums[0] = temp;        k--;    }}Time Limit Exceeded
  

Method 2

The method above does not work. Continue to improve the first method. Cut the vector into the left and right sides.

void rotate(vector
  
    &nums, int k) {    if (nums.size() <= 1) return;    if (k > nums.size()) k %= nums.size();    vector
   
     extra(nums.begin(), nums.begin() + nums.size() - k);    nums.erase(nums.begin(), nums.begin() + nums.size() - k);    nums.insert(nums.end(), extra.begin(), extra.end());}Runtime: 28 ms
   
  

Method 2 Improvement

How about reversing the order?

void rotate(vector
  
    &nums, int k) {    if (nums.size() <= 1) return;    if (k > nums.size()) k %= nums.size();    vector
   
     extra(nums.end() - k, nums.end());    nums.erase(nums.end() - k, nums.end());    nums.insert(nums.begin(), extra.begin(), extra.end());}Runtime: 24 ms
   
  

It takes four seconds to complete.

Method 3

Another method is to use the rotate () function provided by STL ......

void rotate(vector
  
   & nums, int k) {    int len = nums.size();    if (len > 1) {        k %= len;        std::rotate(nums.begin(), nums.end() - k, nums.end());    }}