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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.

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1 Answer 1

Reset to default
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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....

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  • 1
    \$\begingroup\$ 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. \$\endgroup\$ Commented Apr 6, 2015 at 23:04
  • \$\begingroup\$ @rolflWhat if we want to shift it to right? \$\endgroup\$ Commented Nov 30, 2015 at 5:16
  • \$\begingroup\$ @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] \$\endgroup\$ Commented Nov 30, 2015 at 5:26
  • \$\begingroup\$ 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. \$\endgroup\$ Commented May 1, 2016 at 7:17
  • 2
    \$\begingroup\$ @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 \$\endgroup\$ Commented May 1, 2016 at 11:51

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