Given the code fragment: ``java int [] lst = {1, 2, 3, 4, 5, 3, 2, 1}; int sum = 0; for (int frnt = 0, rear = lst.length - 1; frnt < 5 && rear >= 0; frnt++, rear--) { sum = sum + lst[frnt] +…

Question

int [] lst = {1, 2, 3, 4, 5, 3, 2, 1};
int sum = 0;
for (int frnt = 0, rear = lst.length - 1;
 frnt < 5 && rear >= 0;
 frnt++, rear--) {
 sum = sum + lst[frnt] + lst[rear];
}
System.out.print(sum);

Options

• A20
• B25
• C29
• DCompilation fails
• EAnArrayIndexOutOfBoundsException is thrown at runtime

• A
  78% (25)
• B
  13% (4)
• C
  3% (1)
• D
  6% (2)

Explanation

Tracing through this code carefully reveals a discrepancy with the stated answer key - the code as written actually outputs 30, not 20.

Step-by-step trace:

The array {1, 2, 3, 4, 5, 3, 2, 1} has 8 elements (indices 0–7), so rear starts at 7. The loop runs while frnt < 5 && rear >= 0, yielding 5 iterations:

At frnt = 5, the condition 5 < 5 is false and the loop exits. System.out.print(sum) prints 30.

Why the distractors are wrong:

• D (Compilation fails): The code is syntactically valid - declaring two variables in the for-init with the same type is legal Java.
• E (ArrayIndexOutOfBoundsException): All accesses are safe. frnt reaches at most 4 and rear reaches at minimum 3, both valid indices for an 8-element array.
• B (25) and C (29): Neither matches any plausible misreading of the iteration.

Assessment: The stated correct answer of A (20) appears to be an error in the answer key. The answer would be 20 if the original question used a 7-element palindrome {1, 2, 3, 4, 3, 2, 1} with a frnt < rear condition - a likely source of the mistake. As written, the code prints 30.

Memory tip: In two-pointer loops, always check both termination conditions and trace all the way through - especially when the two pointers can "cross" and still satisfy the condition (as frnt=4, rear=3 does here).

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