const findDuplicate = function (nums) {
if (nums.length > 1) {
let slow = nums[0],
fast = nums[nums[0]];
while (slow !== fast) {
slow = nums[slow];
fast = nums[nums[fast]];
}
fast = 0;
while (fast !== slow) {
fast = nums[fast];
slow = nums[slow];
}
return slow;
}
};