链表和数组

[1,2,3,4,5] 1=>2=>3

数组

数据结构的增删改查

arr[0] arr[1] 随机访问O(1)

数组的新增元素复杂度是O(n)

链表

1=>2=>3=>4

随机访问的负复杂度是O(n)

删除和插入元素复杂度是O1

leetcode 203. 移除链表元素

var removeElements = function(head, val) {
  
  // 哨兵 =>1 =>2 =>3
  
  let ele = {
    next: head
  }
  let p = ele
  console.log(p.next)
  while(p.next){
    if(p.next.val === val){
      p.next = p.next.next
    }else{
      p = p.next
    }
  }

  return ele.next
};

leetcode 141. 环形链表

var hasCycle = function(head) {
    let cache = new Set()

    while(head){
        // console.log(cache)
        if(cache.has(head)){
            return true
        }else{
            cache.add(head)
        }
        head = head.next
    }
    return false

    // 双指针思路


//    let slow = head
//    let fast = head

//    while(fast && fast.next){
//        fast = fast.next.next
//        slow = slow.next
//        if(slow === fast) return true

//    }
//     return false


};