What patterns help with string manipulation problems?

Strings are arrays of characters with extra language rules. Before writing code, classify the problem: are you comparing multisets, finding a contiguous substring, matching a pattern, or answering repeated prefix queries? Each classification points to a different technique.

The common techniques

• Frequency map for anagrams, character counts and duplicates
• Two pointers for palindromes and reversing in place
• Sliding window for the longest or shortest valid substring
• Trie for prefix search across many words
• Dynamic programming for edit distance and subsequences

function isAnagram(a, b) {
  if (a.length !== b.length) return false;
  const counts = new Map();
  for (const ch of a) counts.set(ch, (counts.get(ch) || 0) + 1);
  for (const ch of b) {
    if (!counts.has(ch)) return false;
    const next = counts.get(ch) - 1;
    if (next === 0) counts.delete(ch);
    else counts.set(ch, next);
  }
  return counts.size === 0;
}

Be explicit about Unicode. JavaScript string indexing works in UTF-16 code units, so characters outside the basic plane can occupy two code units. For interview answers, mention the assumption and use Array.from when code points matter.