HashTable 解法

#include <iostream>
#include <vector>
#include <unordered_set>

using namespace std;
int n;

int main(void) {
  cin >> n;
  vector<int> nums(n);
  for (int i = 0; i < n; ++i) cin >> nums[i];
  return printf("%d\n", unordered_set<int>(begin(nums), end(nums)).size()), 0;
}