Question

Consider the following method, remDups, which is intended to remove duplicate consecutive elements from nums, an ArrayList of integers. For example, if nums contains {1, 2, 2, 3, 4, 3, 5, 5, 6}, then after executing remDups(nums), nums should contain {1, 2, 3, 4, 3, 5, 6}.
public static void remDups(ArrayList nums)
{
for (int j = 0; j < nums.size() - 1; j++)
{
if (nums.get(j).equals(nums.get(j + 1)))
{
nums.remove(j);
j++;
}
}
}
The code does not always work as intended. Which of the following lists can be passed to remDups to show that the method does NOT work as intended?
A. {1, 1, 2, 3, 3, 4, 5}
B. {1, 2, 2, 3, 3, 4, 5}
C. {1, 2, 2, 3, 4, 4, 5}
D. {1, 2, 2, 3, 4, 5, 5}
E. {1, 2, 3, 3, 4, 5, 5}

Answer 1

Answer:

B. {1, 2, 2, 3, 3, 4, 5}

Explanation:

Given

The above code segment

Required

Determine which list does not work

The list that didn't work is $B.\ \{1, 2, 2, 3, 3, 4, 5\}$

Considering options (A) to (E), we notice that only list B has consecutive duplicate numbers i.e. 2,2 and 3,3

All other list do not have consecutive duplicate numbers

Option B can be represented as:

$nums[0] = 1$

$nums[1] = 2$

$nums[2] = 2$

$nums[3] = 3$

$nums[4] = 3$

$nums[5] = 4$

$nums[6] = 5$

if (nums.get(j).equals(nums.get(j + 1)))

The above if condition checks for duplicate numbers.

In (B), when the elements at index 1 and 2 (i.e. 2 and 2) are compared, one of the 2's is removed and the Arraylist becomes:

$nums[0] = 1$

$nums[1] = 2$

$nums[2] = 3$

$nums[3] = 3$

$nums[4] = 4$

$nums[5] = 5$

The next comparison is: index 3 and 4. Meaning that comparison of index 2 and 3 has been skipped.

This is so because of the way the if statement is constructed.