Contains Duplicate

 https://leetcode.com/problems/contains-duplicate/

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        int n = nums.size();
        unordered_map<int,int>m;
        for(int i = 0; i < n; i++)
        {
            if(m.find(nums[i]) == m.end())
                m[nums[i]]++;
            else 
                return true;
        }
        return false;
  }
};

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        int n = nums.size();
        sort(nums.begin(), nums.end());
        for(int i = 0; i < n-1; i++)
            if(nums[i] == nums[i+1])
                return true;
        return false;
    }
};

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