Skip to main content

9. Group Anagrams

mediumAsked at Adyen

Group strings that are anagrams of each other into the same bucket.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given an array of strings, group the anagrams together. Return the answer in any order.

Constraints

  • 1 <= strs.length <= 10^4
  • 0 <= strs[i].length <= 100
  • Lowercase English letters.

Examples

Example 1

Input
strs = ["eat","tea","tan","ate","nat","bat"]
Output
[["bat"],["nat","tan"],["ate","eat","tea"]]

Example 2

Input
strs = [""]
Output
[[""]]

Approaches

1. Sort-key grouping

Group by sorted-character string.

Time
O(n * k log k)
Space
O(n * k)
const map = new Map();
for (const s of strs) {
  const key = [...s].sort().join('');
  if (!map.has(key)) map.set(key, []);
  map.get(key).push(s);
}
return [...map.values()];

Tradeoff:

2. Count-vector key

Hash a 26-length frequency array as the bucket key.

Time
O(n * k)
Space
O(n * k)
function groupAnagrams(strs) {
  const map = new Map();
  for (const s of strs) {
    const c = new Array(26).fill(0);
    for (const ch of s) c[ch.charCodeAt(0) - 97]++;
    const key = c.join(',');
    if (!map.has(key)) map.set(key, []);
    map.get(key).push(s);
  }
  return [...map.values()];
}

Tradeoff:

Adyen-specific tips

Adyen rewards hashing a count vector over sorting since their fraud-signal pipelines bucket transaction fingerprints under similar O(k) constraints.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Group Anagrams and other Adyen interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →