0287-find-the-duplicate-number.ts

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     val: number
 *     next: ListNode | null
 *     constructor(val?: number, next?: ListNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.next = (next===undefined ? null : next)
 *     }
 * }
 */

function findDuplicate(nums: number[]): number {
    let slow = 0;
    let fast = 0;
    while (true) {
        slow = nums[slow];
        fast = nums[nums[fast]];
        if (slow == fast) {
            break;
        }
    }
    let slow2 = 0;

    while (true) {
        slow = nums[slow];
        slow2 = nums[slow2];
        if (slow == slow2) {
            break;
        }
    }
    return slow;
}