日常刷题0x4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：剑指 Offer 59 - II

// 剑指 Offer 59 - II
var MaxQueue = function () {
    this.queue = []
    this.maxIdx = -1
};

/**
 * @return {number}
 */
MaxQueue.prototype.max_value = function () {
    if (this.queue.length == 0) {
        return -1
    } else {
        return this.queue[this.maxIdx]
    }
};

/** 
 * @param {number} value
 * @return {void}
 */
MaxQueue.prototype.push_back = function (value) {
    this.queue.push(value)
    if (this.maxIdx == -1) {
        this.maxIdx = 0
    } else {
        if (value > this.queue[this.maxIdx]) {
            this.maxIdx = this.queue.length - 1
        }
    }
};

/**
 * @return {number}
 */
MaxQueue.prototype.pop_front = function () {
    if (this.queue.length == 0) {
        return -1
    } else {
        this.maxIdx--
        let shiftValue = this.queue.shift()
        if (this.maxIdx == -1) {
            //找最大值
            this.findMaxValue()
        }
        return shiftValue
    }
};

MaxQueue.prototype.findMaxValue = function () {
    this.maxIdx = 0
    for (let i = 1; i < this.queue.length; i++) {
        if (this.queue[i] > this.queue[this.maxIdx]) {
            this.maxIdx = i
        }
    }
}

题号：剑指offer 22

//剑指offer 22
//2次遍历
var getKthFromEnd = function (head, k) {
    let total = 0, dumyNode = new ListNode(-1)
    dumyNode.next = head, curNode = dumyNode
    //找节点总数
    while (curNode.next) {
        total++
        curNode = curNode.next
    }
    curNode = dumyNode
    let step = total - k + 1
    while (step != 0) {
        curNode = curNode.next
        step--
    }
    return curNode
};

//利用栈
var getKthFromEnd = function (head, k) {
    let stack = [], curNode = head
    while (curNode) {
        stack.push(curNode)
        curNode = curNode.next
    }
    while (k != 1) {
        stack.pop()
        k--
    }
    return stack.pop()
};

//利用递归
var getKthFromEnd = function (head, k) {

    let result = null
    let helper = (node) => {
        if (node == null) {
            return
        }
        helper(node.next)
        k--
        if (k == 0) {
            result = node
        }
    }
    helper(head)
    return result
};

题号：7

var reverse = function (x) {

    let result = 0, max = Math.pow(2, 31) - 1, min = -Math.pow(2, 31)
    do {
        let tmp = x % 10 //得到末尾余数
        result = result * 10 + tmp
        if (result > max || result < min) {
            return 0
        }
        //减去余数然后/10挤掉末尾数字
        x -= tmp
        x /= 10
    } while (x != 0);
    return result
};