Spot the bug - #30

programming web dev
1

There is one subtle logic bug.

function hasDuplicate(nums) {
  const seen = new Set();
  for (const n of nums) {
    if (seen.has(n)) {
      return false;
    }
    seen.add(n);
  }
  return true;
}

console.log(hasDuplicate([2, 7, 4, 7]));

Reply with what is broken and how you would fix it.

1 Like
2

The return values are backwards. Hitting seen.has(n) means you found a duplicate, so that should return true, and the “made it through the loop” case should return false.

function hasDuplicate(nums) {
  const seen = new Set();
  for (const n of nums) {
    if (seen.has(n)) return true;
    seen.add(n);
  }
  return false;
}

Right now it’s basically saying “duplicate found → false” and “no duplicates → true,” which is the opposite of what the function name implies.

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