287. Find the Duplicate Number

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.


class Solution {
public:
    int findDuplicate(vector<int>& nums) {
        int n = nums.size();
        
        for(int i = 0; i < n; ++i)
        {
            int idx = abs(nums[i]);
            
            if(nums[idx] < 0)
                return idx;
            
            nums[idx] = -nums[idx];
        }
        
        return n;
    }
    
};