LeetCode 每日 [ 2022 - 02 - 17 ]

合并两个有序链表

• 虚拟头节点 + 指针

  /**
   * 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) {
    const dummyHead = new ListNode(0, list1);
    let current = dummyHead;
  
    while(list1 !== null && list2 !== null) {
      if(list1.val < list2.val) {
        current.next = list1;
        list1 = list1.next;
      } else {
        current.next = list2;
        list2 = list2.next;
      }
      current = current.next;
    }
  
    current.next = list1 === null? list2 : list1;
  
    return dummyHead.next;
  };

• 递归法

  /**
   * 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) {
      // 递归结束条件
      if(list1 === null) return list2;
      if(list2 === null) return list1;
  
      if(list1.val < list2.val) {
          list1.next = mergeTwoLists(list1.next, list2);
          return list1;
      } else {
          list2.next = mergeTwoLists(list1, list2.next);
          return list2;
      }
  };

移除链表元素

• 虚拟头节点

  /**
   * Definition for singly-linked list.
   * function ListNode(val, next) {
   *     this.val = (val===undefined ? 0 : val)
   *     this.next = (next===undefined ? null : next)
   * }
   */
  /**
   * @param {ListNode} head
   * @param {number} val
   * @return {ListNode}
   */
  var removeElements = function(head, val) {
    // 虚拟头节点
    const dummyHead = new ListNode(0, head);
    let current = dummyHead;
  
    while(current && current.next) {
      // 只需找到要删除的节点的上一个节点
      if(current.next.val === val) current.next = current.next.next;
      else current = current.next;
    }
  
    return dummyHead.next;
  };

删除排序链表中的重复元素 II

• 虚拟头节点 + 循环判断相等

  /**
   * Definition for singly-linked list.
   * function ListNode(val, next) {
   *     this.val = (val===undefined ? 0 : val)
   *     this.next = (next===undefined ? null : next)
   * }
   */
  /**
   * @param {ListNode} head
   * @return {ListNode}
   */
  var deleteDuplicates = function(head) {
      if(!(head && head.next)) return head;
  
      const dummyHead = new ListNode(0, head);
      let current = dummyHead;
  
      while(current.next && current.next.next) {
          if(current.next.val === current.next.next.val) {
              const val = current.next.val;
  
              while(current.next && current.next.val === val) {
                  current.next = current.next.next;
              }
          } else {
              current = current.next;
          }
      }
  
      return dummyHead.next;
  };

• 哈希表 + 两次遍历