Find the Duplicate Number
Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one. Example 1: Input: [1,3,4,2,2] Output: 2 Example 2: Input: [3,1,3,4,2] Output: 3 Note: You must not modify the array (assume the array is read only). You must use only constant, O (1) extra space. Your runtime complexity should be less than O ( n 2 ). There is only one duplicate number in the array, but it could be repeated more than once. METHOD 1: class Solution { public int findDuplicate(int[] nums) { ArrayList<Integer>list = new ArrayList<Integer>(); for(int num:nums){ if(list.contains(num)){ return num; } else{ list.add(num); } } return -1; } } Try it on Leetcode Here, we are doing with