Contains Duplicate

HardArrays & Hashing

The problem

Given an integer array, return true if any value appears at least twice, and false if every element is distinct.

An empty array and a single-element array are both distinct, so both return false.

containsDuplicate({1, 2, 3, 1})

One of these three is correct

Two lines apart, at the closest.

The wrong ones are this same code with between two and five lines changed. Some of those changes do not compile. There is no Run button: running all three would turn this into a vote rather than a reading.

1	bool containsDuplicate(const vector<int>& nums) {
2
3	unordered_set<int> seen;
4
5	for (int x : nums) {
6	if (!(seen.count(x))) {
7	return true;
8	}
9	}
10
11	return false;
12	}

1	bool containsDuplicate(const vector<int>& nums) {
2
3	unordered_set<int> seen;
4
5	for (int x : nums) {
6	if (seen.count(x)) {
7	return true;
8	}
9	seen.insert(x);
10	}
11
12	return false;
13	}

1	bool containsDuplicate(const vector<int>& nums) {
2
3	unordered_set<int> seen;
4
5	for (int x : nums) {
6	if (!(seen.count(x))) {
7	return true;
8	}
9	}
10
11	return true;
12	}