day4打卡

5. 两两交换链表中的节点

1. 递归法

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var swapPairs = function(head) {
    if (head === null|| head.next === null) {
        return head;
    }
    const newHead = head.next;
    head.next = swapPairs(newHead.next);
    newHead.next = head;
    return newHead;
};

2. 迭代法

6. 删除链表的倒数第n个节点

1. 快慢指针

/**
 * @param {ListNode} head
 * @param {number} n
 * @return {ListNode}
 */
var removeNthFromEnd = function(head, n) {
let slow = head, fast = head;
    while(n--) {
        fast = fast.next;
    }
    if(!fast) {
        return head.next;
    }
    while(fast.next) {
        slow = slow.next;
        fast = fast.next;
    }
    slow.next = slow.next.next;
    return head;
};

7. 链表相交

1. 哈西集合方法

var getIntersectionNode = function(headA, headB) {
    const visited = new Set();
    let temp = headA;
    while (temp !== null) {
        visited.add(temp);
        temp = temp.next;
    }
    temp = headB;
    while (temp !== null) {
        if (visited.has(temp)) {
            return temp;
        }
        temp = temp.next;
    }
    return null;    
};

8. 环形链表

1. 哈希表法

var detectCycle = function(head) {
    const visited = new Set();
    while (head !== null) {
        if (visited.has(head)) {
            return head;
        }
        visited.add(head);
        head = head.next;
    }
    return null;
};