JS 链表

链表题的一些总结

两种链表定义

• class

class ListNode {
  val;
  next = null;
  constructor(value) {
    this.val = value;
    this.next = null;
  }
}

• function

function ListNode(val, next) {
  this.val = val === undefined ? 0 : val;
  this.next = next === undefined ? null : next;
}

set存储链表节点，存的是整个空间

• 相交链表

/**
 * 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) {
    const set = new Set();
    let tmp = headA;
    while(tmp) {
        if(!set.has(tmp)) {
            set.add(tmp);
        }
        tmp = tmp.next;
    }

    tmp = headB;
    while(tmp) {
       if(set.has(tmp)) {
            return tmp;
        }
        tmp = tmp.next;  
    }
    return null;
};

同时处理长短不一的两个链表

处理方法 while(l1 || l2)

• 两数相加

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function(l1, l2) {
    let head = new ListNode(0);
    let cur = head;
    let carry = 0;

    while(l1 != null || l2 != null) {
        const n1 = l1 != null ? l1.val : 0;
        const n2 = l2 != null ? l2.val : 0;

        let sum = n1 + n2 + carry;
        carry = Math.floor(sum / 10);
        sum = sum % 10;

        let tmp = new ListNode(sum, null);
        cur.next = tmp;
        cur = tmp;

        if(l1 != null) {
            l1 = l1.next;
        }

        if(l2 != null) {
            l2 = l2.next;
        }
    }

    if(carry === 1) {
        let tmp = new ListNode(1, null);
        cur.next = tmp;
        cur = tmp;
    }

    return head.next;
};

处理方法 while(l1 & l2)

不能用或，如果一个链表之后为空了，就没有比较的必要

• 合并有序链表
• 超出时间限制

var mergeTwoLists = function(list1, list2) {
    let dummyhead = new ListNode(-1);
    let h = dummyhead;
    while(list1 || list2) {
        if(list1 === null) {
            h.next = list2;
        } else if(list2 === null) {
            h.next = list1;
        } else {
            if(list1.val < list2.val) {
                h.next = list1;
                h = list1;
                list1 = list1.next;
            } else {
                h.next = list2;
                h = list2;
                list2 = list2.next;
            }
        }
    }
    return h.next;
};

• 不超出时间限制

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} list1
 * @param {ListNode} list2
 * @return {ListNode}
 */
var mergeTwoLists = function(list1, list2) {
    let dummyhead = new ListNode(-1);
    let h = dummyhead;

    while(list1 && list2) {
        if(list1.val < list2.val) {
            h.next = list1;
            h = list1;
            list1 = list1.next;
        } else {
            h.next = list2;
            h = list2;
            list2 = list2.next;
        }
    }
    if(list1 === null) {
        h.next = list2;
    } else if(list2 === null) {
        h.next = list1;
    }

    return dummyhead.next;
};

dummyhead的使用

返回时 dummyhead.next

JS搭配hashmap搭配链表的时候

如果原链表的 random 指针为 null，map.get(cur.random) 会返回 undefined，而不是 null。这可能会导致新链表的 random 指针指向错误。

• 138随机链表的复制

var copyRandomList = function(head) {
    if(head === null) {
        return null;
    }
    const map = new Map();
    let cur = head;
    while(cur !== null) {
        map.set(cur, new _Node(cur.val, null, null));
        cur = cur.next;
    }

    cur = head;
    while(cur !== null) {
        // 显式处理 next 和 random 为 null 的情况
        map.get(cur).next = cur.next ? map.get(cur.next) : null;
        map.get(cur).random = cur.random ? map.get(cur.random) : null;
        cur = cur.next;
    }

    return map.get(head);
};