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]. How many different ways do you know to solve this problem?

Using intermediate array

  1. First find out correct number of rotations using mod
  2. Create temporary array
  3. Push array elements into that temporary array
  4. Copy that temporary array into  original array
function rotateArray(nums,k) {
    if(isNaN(k) || k < 0) {
      throw "provide valid order";
    }

    if(nums.length == 0) {
      throw "provide valid array";
    }

    if(k > nums.length) 
        k=k%nums.length;
 
    var result = [];
 
    for(var i=0; i < k; i++){
        result[i] = nums[nums.length-k+i];
    }
 
    var j=0;
    for(var i=k; i<nums.length; i++){
        result[i] = nums[j];
        j++;
    }
 
    nums = result.slice();
    console.log(nums);
}

Complexity

Observe above demo. It will take O(n) space and O(n) time

Using bubble rotate

By using bubble swap, we can solve this problem. Move array elements from right side to left side of the array using bubble swap
function rotateArray2(arr, order) {
    if(isNaN(order) || order < 0) {
      throw "provide valid order";
    }

    if(arr.length == 0) {
      throw "provide valid array";
    }
    for (var i = 0; i < order; i++) {
        for (var j = arr.length - 1; j > 0; j--) {
            var temp = arr[j];
            arr[j] = arr[j - 1];
            arr[j - 1] = temp;
        }
    }
  console.log(arr);
}

Complexity

Observe above demo. It will take O(1) space and O(n*k) time

Using Reversal

Divide array into 2 parts based on given order. Reverse first part and then reverse second, then reverse whole array  
function rotate3(arr, order) {
    if(isNaN(order) || order < 0) {
      throw "provide valid order";
    }

    if(nums.length == 0) {
      throw "provide valid array";
    }
    
    order = order % arr.length;
 
    //length of first part
    var a = arr.length - order; 
 
    reverse(arr, 0, a-1);
    reverse(arr, a, arr.length-1);
    reverse(arr, 0, arr.length-1);
 console.log(arr);
}
 
function reverse(arr, left, right){
    while(left < right){
        var temp = arr[left];
        arr[left] = arr[right];
        arr[right] = temp;
        left++;
        right--;
    }   
}

rotate3([1,2,3,4,5,6],3);

Complexity

Observe above demo. It will take O(1) space and O(n) time

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