Implement a uniq-like function
Company: Vanta
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
Implement a function similar to the Unix `uniq` utility.
You are given a sequence of strings representing lines of text in the order they appear in a file. Return a new sequence where **only consecutive duplicate lines are collapsed** into a single line (i.e., remove repeated adjacent duplicates but do not remove duplicates that are separated by different lines).
Example:
- Input: `["a","a","b","b","b","a","a","c"]`
- Output: `["a","b","a","c"]`
Clarify with the interviewer:
- Whether input is streaming (iterator) or in-memory.
- Whether comparison is case-sensitive.
- Whether to support options like returning counts per group (e.g., `uniq -c`) or only the collapsed lines.
Overview: This question evaluates a candidate's ability in sequence and string processing, including managing state across adjacent elements and handling interface assumptions such as streaming versus in-memory input and case-sensitive comparisons; it belongs to the Coding & Algorithms category and the string-manipulation/data-processing domain.
Implement a function similar to the Unix `uniq` utility.
You are given an in-memory list of strings representing lines of text in the order they appear in a file. Return a new list where only consecutive duplicate lines are collapsed into a single line.
Important: only adjacent duplicates should be removed. If the same line appears again later after a different line, it should remain in the result.
Assume comparisons are case-sensitive, and you only need to return the collapsed lines (not counts).
Constraints
- 0 <= len(lines) <= 100000
- Each element of `lines` is a string
- Comparison is case-sensitive
- Return only the collapsed lines; do not return counts
Examples
Input: ["a", "a", "b", "b", "b", "a", "a", "c"]
Expected Output: ["a", "b", "a", "c"]
Explanation: Consecutive duplicates are collapsed, but the later `a` group is kept because it is separated by `b`.
Input: []
Expected Output: []
Explanation: Empty input should return an empty list.
Hints
- You only need to compare each line with the most recently kept line.
- Be careful with the first element and with empty input.
Community answers
Answer by sasha
public class Unique {
public static String unique(String str) {
if ( str == null || str .isEmpty()) {
return str;
}
StringBuilder buf = new StringBuilder();
char prev = ' ';
for ( char cur : str.toCharArray() ){
if (cur == prev) continue;
buf.append(cur);
prev = cur;
}
return buf.toString();
}
public static void main(String arg []) {
String str = "cvfaaaabfbbbcccaaabbb";
String expected = "cvfabfbcab";
String found = unique(str);
System.out.println("Both expected = found " + expected.equals(found));
System.out.println("found =>" + found);
}
}