面试算法总结之链表篇 (javascript)

• 链表相关算法总结

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1、链表的中间节点
2、相交链表
3、删除链表的节点
4、反转链表
5、反转链表2（这里是具体的讲解与过程）
6、链表的倒数第k个节点 （这里是具体的讲解）
7、环形链表
8、回文链表

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1、链表的中间节点（跳转到博客）

var middleNode = function(head) {
    slow = fast = head;
    while (fast && fast.next) {
        slow = slow.next;
        fast = fast.next.next;
    }
    return slow;
};

2、相交链表 （跳转博客）

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} headA
 * @param {ListNode} headB
 * @return {ListNode}
 */
var getIntersectionNode = function(headA, headB) {
    // 清除高度差
    let pA = headA, pB = headB
    while(pA || pB) {
        if(pA === pB) return pA
        pA = pA === null ? headB : pA.next
        pB = pB === null ? headA : pB.next
    }
    return null
};

3、删除链表的节点 （跳转博客）

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} val
 * @return {ListNode}
 */
var deleteNode = function(head, val) {
    var prev = new ListNode(-1)
    prev.next = head
    var node = prev
    while(node.next ){
        if(node.next.val === val){
            node.next = node.next.next
            break
        }
        node  = node.next
    }
    
    return prev.next
};

4、反转链表

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var reverseList = function(head) {
    var prev = null,cur=head,temp;
    while(cur){
        temp = cur.next;//修改前先记住下一个节点
        cur.next = prev; //改别指向，第一个节点prev是null,
        prev = cur; //记录前一个节点，供下次循环使用
        cur = temp; // cur通过temp指向下一节点
    }
    return prev;//cur会多循环直到null
};

5、反转部分链表

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} m
 * @param {number} n
 * @return {ListNode}
 */
var reverseBetween = function(head, m, n) {
    if(m===n) return head
    let dummy=new ListNode(0);
    dummy.next=head;
    let d = dummy,a = dummy
    for(let i= 0 ; i < m-1 ; i++) a = a.next
    for(let j = 0 ; j < n ; j++) d = d.next
     let b=a.next ,c=d.next;
    for( p=b,q=p.next;q!==c;){
        o = q.next
        q.next = p
        p = q
        q = o
    }
    a.next = d
    b.next = c

    return dummy.next
}

6、删除倒数第k个节点 （跳转博客）

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var getKthFromEnd = function(head, k) {
{
    var result = [];
    while(head) {
        result.unshift(head);
        head = head.next
    }
    return result[k-1];
}}


/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var getKthFromEnd = function(head, k) {
    if(k <=0 || !head || !k ){
        return null;
    }
    var fast = head;
    var slow = head;
    for(let i =0 ; i < k-1 ; i++){
         if (fast.next) {
            fast = fast.next
        } else {
            return null
        }
    }
    while(fast.next){
        fast = fast.next;
        slow = slow.next;
    }
    return slow

};

7、环形链表（龟兔赛跑的思路）

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

/**
 * @param {ListNode} head
 * @return {boolean}
 */
var hasCycle = function(head) {
    if(!head || !head.next){return false}
    var slow = head
    var fast = head.next
    while(slow!==fast){
        if(!fast || !fast.next){
        return false
        }
        slow = slow.next
        fast = fast.next.next
    }
    return true
};

8、回文链表

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {boolean}
 */
var isPalindrome = function(head) {
    var arr=[];
    while(head){
        arr.push(head.val);
        head=head.next;
    }
    return arr.toString() === arr.reverse().toString();
};