Spot the bug - #45

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 bug is just the boolean logic vs the function name: you’re returning false when you do find a duplicate, and true when you never find one. So hasDuplicate([2, 7, 4, 7]) prints false even though 7 repeats.

Swap the return values so the “already seen” branch returns true, and the fall-through returns false:

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