LeetCode 217. Contains Duplicate

Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct.

// HashMap

#include <iostream>
#include <vector>
#include <set>
using namespace std;

bool containsDuplicates(vector<int>& nums) {
if(nums.size() == 0) return false;
set<int> hashMap;
for(int i = 0; i < nums.size(); ++i) {
if(hashMap.find(nums[i]) == hashMap.end()) {
hashMap.insert(nums[i]);
} else {return true;}
}
return false;
}

int main(void) {<pre name="code" class="cpp">    bool containsDuplicate(vector<int>& nums) {
if(nums.size() <= 1) return false;
sort(nums.begin(), nums.end());
int i = 0, j = 1;
while(j < nums.size()) {
if(nums[i] == nums[j]) return true;
else {
i = j;
j++;
}
}
return false;
}

Second Method: Two Pointers.

Time Complexity O(nlgn), Space O(1)

bool containsDuplicate(vector<int>& nums) {
if(nums.size() <= 1) return false;
sort(nums.begin(), nums.end());
int i = 0, j = 1;
while(j < nums.size()) {
if(nums[i] == nums[j]) return true;
else {
i = j;
j++;
}
}
return false;
}