#287 - Find the Duplicate Number

Medium • View on LeetCode • View on GitHub

Problem Description

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 using only constant extra space.

Solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var findDuplicate = function(nums) {
  let slow = nums[0];
  let fast = nums[nums[0]];

  while (slow !== fast) {
    slow = nums[slow];
    fast = nums[nums[fast]];
  }
  slow = 0;
  while (slow !== fast) {
    slow = nums[slow];
    fast = nums[fast];
  }

  return slow;
};