Spot the bug - #84

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.

2

Your return values are flipped relative to the function name/intent. Right now it returns false when it finds a duplicate, and true when it gets through the loop without finding one. Fix it by returning true on the duplicate branch and false at the end:

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

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

Confidence: high.