Duplicate Zeros

EasyTwo Pointerstwo pointers

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given a fixed-length integer array arr, write a second copy of every 0 immediately after it, shifting the remaining elements to the right. The array's length does not change: elements pushed past the end are dropped. Perform the change **in place** (no extra array proportional to n) and return arr so it can be checked.

Examples

Input: arr = [1,0,2,3,0,4,5,0]
Output: [1,0,0,2,3,0,0,4]
Both early zeros are doubled; 5 and the final 0 are pushed off the end.
Input: arr = [1,2,3]
Output: [1,2,3]
No zeros, nothing changes.
Input: arr = [8,4,5,0,0,0,0,7]
Output: [8,4,5,0,0,0,0,0]
Only the first two zeros fit with their copies; the third 0 fits once, the rest is cut off.

Constraints

  • 1 <= arr.length <= 10^4
  • 0 <= arr[i] <= 9

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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