Patterns

Build a Set of seen items; check membership in O(1)

When to useDetect duplicates, set intersection/union, check if element exists

iterative

INITIALIZE

empty Set

const vowels = new Set(['a','e','i','o','u']);
let count = 0;

const set = new Set();

const seen = new Set();

const seen = new Set();

—

const numSet = new Set(nums);
let result = 0;

const positions = new Set(intList);
let result = '';

TRAVERSE

for-of input

for (const ch of s.toLowerCase()) {

for (const value of arr) {

for (const n of arr) {

for (const n of nums) {

—

for (const n of nums) {

for (let i = 0; i < n; i++) {

[CHECK]

check has(); add to set

  if (vowels.has(ch)) count++;

  set.add(value);

  seen.add(n);

  if (seen.has(n)) return true;
  seen.add(n);

  const word = s.slice(si, end);
  if (usedWords.has(word)) continue;

  if (n > 0 && numSet.has(-n)) result = Math.max(result, n);

  result += positions.has(i) ? '+' : '-';

RETURN

result (often early exit on hit)

return count;

return set.has(target);

return [...seen];

return false;

return false;

return result;

return result;