49. Group Anagrams

Group the strings that are anagrams of each other. The groups may be returned in any order.

Anagrams also share the same 26 letter counts. Encoding the counts as a key avoids sorting each word.

1function groupAnagrams(strs: string[]): string[][] {
2  const groups = new Map<string, string[]>();
3  for (const w of strs) {
4    const cnt = new Array(26).fill(0);
5    for (const ch of w) cnt[ch.charCodeAt(0) - 97]++;
6    const key = cnt.join("#");
7    if (!groups.has(key)) groups.set(key, []);
8    groups.get(key)!.push(w);
9  }
10  return [...groups.values()];
11}

strs

eat

tea

tan

ate

nat

bat

groups (key = letter counts)

empty

Empty map.

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