217. Contains Duplicate

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

• Time : O(n)
• Space : O(n)

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        unordered_set<int> s;
        for(auto& n : nums) {
            if(s.count(n)) return true;
            s.insert(n);
        }
        return false;
    }
};

• Time : O(nlogn)
• Space : O(1)

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        for(int i = 1; i < nums.size(); i++) {
            if(nums[i] == nums[i-1])return true;
        }
        return false;
    }
};

• Time : O(n)
• Space : O(n)

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        return nums.size() != unordered_set<int>(nums.begin(), nums.end()).size();
    }
};