日常刷题0x2之德玛蹲草丛

此阶段给自己定的目标是：做过的这些题每天坚持继续刷二遍，每道题做过之后开始尝试多解法尝试解题。上一阶段是感知都有什么题目，此阶段主要系统化常规题解套路知识，牢记牢记此阶段目的。

题号：938

var rangeSumBST = function (root, low, high) {

    let result = 0
    //中序遍历
    let helper = (node) => {
        if (node == null) {
            return
        }
        helper(node.left)
        //处理当前节点
        if (node.val >= low && node.val <= high) {
            result += node.val
        }
        helper(node.right)
    }
    helper(root)
    return result
};

题号：460

var LFUCache = function (capacity) {
    //记录最大容量
    this.capacity = capacity
    //记录缓存数据
    this.lists = []
    //标识一个最近的时间戳
    //记录最近一次操作的时间
    this.latesttime = null
};


LFUCache.prototype.get = function (key) {
    let obj = this.findObj(key)
    if (obj) {
        obj.count++
        //更新时间
        this.latesttime++
        obj.time = this.latesttime
        this.sortLists()
        return obj.value
    } else {
        return -1
    }
};

LFUCache.prototype.put = function (key, value) {

    if (this.capacity == 0) {
        //do nothing
        return
    }
    let obj = this.findObj(key)
    if (obj) {
        //update value
        obj.count++
        this.latesttime++
        obj.time = this.latesttime
        obj.value = value
    } else {
        if (this.lists.length == this.capacity) {
            this.lists.shift()
        }
        //insert value
        let obj = {}
        obj.key = key
        obj.count = 1
        if (this.latesttime == null) {
            this.latesttime = 10086
        } else {
            this.latesttime++
        }
        obj.time = this.latesttime
        obj.value = value
        this.lists.push(obj)
    }
    //sort value
    this.sortLists()
};

LFUCache.prototype.findObj = function (key) {
    for (let i = 0; i < this.lists.length; i++) {
        let obj = this.lists[i]
        if (obj.key === key) {
            return obj
        }
    }
    return null
}

LFUCache.prototype.sortLists = function () {
    this.lists.sort((a, b) => {
        if (a.count - b.count == 0) {
            return a.time - b.time
        }
        return a.count - b.count
    })
}

题号：148

var sortList = function (head) {
// 开辟一个数组空间
    let arr = []
    while (head) {
        arr.push(head)
        head = head.next
    }
    //排序数组中节点
    arr.sort((a, b) => {
        return a.val - b.val
    })
    //遍历数组设置next指针
    for (let i = 0; i < arr.length; i++) {
        let curNode = arr[i]
        if (i > 0) {
            let preNode = arr[i - 1]
            preNode.next = curNode
        }
        curNode.next = null
    }
    return arr[0] ? arr[0] : null
};

//递归归并排序
var sortList = function (head) {
    if (head == null) {
        return null
    }
    if (head.next == null) {
        return head
    }
    //快慢指针找中点
    let slow = head, fast = head.next
    while (fast && fast.next) {
        fast = fast.next.next
        slow = slow.next
    }
    //从slow处断开
    let tmp = slow.next
    slow.next = null
    //去排序左边的链表
    let list1 = sortList(head)
    //去排序右边的链表
    let list2 = sortList(tmp)
    //合并有序链表
    //排完序合并左右序列
    //设置一个头结点方便下面的逻辑处理
    let result = new ListNode()
    let curNode = result
    while (list1 && list2) {
        if (list1.val > list2.val) {
            curNode.next = list2
            curNode = list2
            list2 = list2.next
        } else {
            curNode.next = list1
            curNode = list1
            list1 = list1.next
        }
        curNode.next = null
    }
    if (list1) {
        curNode.next = list1
    }
    if (list2) {
        curNode.next = list2
    }
    return result.next
};