주기 LinkedList 감지 - I

접근법 1

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} head
 * @return {boolean}
 */
var hasCycle = function(head) {

    let tempNode = new ListNode(0);
    let current = head;

    while(current){
        if(current.next === tempNode){
            return true;
        }
        let saveNext = current.next;
        current.next = tempNode;
        current = saveNext;
    }
    return false;
};

접근법 2

var hasCycle = function(head) {
    let mapValues = new Map();
    while (head) {
        if (mapValues.has(head)) {
            return true;
        } else {
            mapValues.set(head, "Yes");
            head = head.next;
        }
    }

    return false;

};

접근법 3