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287. Find the Duplicate Number

Question​

Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.

There is only one repeated number in nums, return this repeated number.

You must solve the problem without modifying the array nums and uses only constant extra space.

Example 1:

Input: nums = [1,3,4,2,2]
Output: 2

Example 2:

Input: nums = [3,1,3,4,2]
Output: 3

Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times.

Approach​

Solution​

//NOT THE BEST SOLUTION, PURE BRUT FORCE
class Solution {
public:
    int findDuplicate(vector<int>& nums) {
        unordered_map<int,int> m;
        int out;
        for(auto n : nums){
            m[n]++;
        }
        for(auto mE: m){
            if(mE.second > 1) out= mE.first;
        }
        return out;
    }
};