LeetCode-in-All

287. Find the Duplicate Number

Medium

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

Example 3:

Input: nums = [1,1]

Output: 1

Example 4:

Input: nums = [1,1,2]

Output: 1

Constraints:

Follow up:

Solution

public class Solution {
    public int FindDuplicate(int[] nums) {
        int[] arr = new int[nums.Length + 1];
        foreach (int num in nums) {
            arr[num] += 1;
            if (arr[num] == 2) {
                return num;
            }
        }
        return 0;
    }
}