Left Shifting an array of ints

Question

The problem I am referring to is here

So basically it's about shifting an array of ints 1 position to the left and relocating the lost first int in the start of the array to the last position at the right:

\$\mathrm{shiftLeft}(\{6, 2, 5, 3\}) → \{2, 5, 3, 6\}\$

\$\mathrm{shiftLeft}(\{1, 2\}) → \{2, 1\}\$

\$\mathrm{shiftLeft}(\{1\}) → \{1\}\$

Please feel free to review the code below:

public int[] shiftLeft(int[] nums) {
 for(int i = 0, start = 0; i < nums.length; i++)
 {
 if(i == 0)
 start = nums[i];
 if(i == (nums.length -1))
 {
 nums[i] = start;
 break;
 } 
 nums[i] = nums[i + 1];
 }
 return nums; 
}

Also I would like to get rid of the variable start and try to solve it only using the loop iterator i, any suggestions are welcome.

Answer 1

Your current solution is actually pretty good, conceptually. There's nothing wrong with the start variable. I am not sure why you want to remove it. The loop is logically a good solution, but there's a better way than that, though (better because you can make the system do it for you....).

public int[] shiftLeft(int[] nums) {
 if (nums == null || nums.length <= 1) {
 return nums;
 }
 int start = nums[0];
 System.arraycopy(nums, 1, nums, 0, nums.length - 1);
 nums[nums.length - 1] = start;
 return nums;
}

Note that, in addition to using System.arraycopy I also check to see that the input has valid values available....

• maaartinus: I'd omit the nums == null check. Your method is null-safe, but most Java methods are not, which means that the programmer must handle nulls somewhere. If they don't, they'll get an NPE and the sooner the better.
• paul: @rolflWhat if we want to shift it to right?
• rolfl: @paul - then adjust the indices you see in the code to be in the other direction.... so, for example instead of int start = nums[0] have int start = nums[nums.length - 1]
• Mona Jalal: what if we want to shift it 50 times to the left but array length is 20!? your solution would have a bug then I'd say.
• rolfl: @MonaJalal - well, no.... it has no bug. Your comment makes no sense. The original question is to only shift by 1, and there is not even an argument/parameter to specify any other shift distance. The only way to shift by 50 is to call the method 50 times, and it will work just fine then