刷题5 剑指 Offer — 栈和队列

剑指 Offer 06. 从尾到头打印链表

https://leetcode-cn.com/leetbook/read/illustrate-lcof/xs92sh/

• 方法一：reverse()

var reversePrint = function(head) {
    var stack = [];
    while(head != null){
        stack.push(head.val);
        head = head.next
    }
    //return stack.reverse()
};

• 方法二：栈（先进后出，push+pop）

var reversePrint = function(head) {
    var stack = [];
    while(head != null){
        stack.push(head.val);
        head = head.next;
    }
    var res = [];
    const len = stack.length; //需要初始stack的长度
    for(var i = 0; i< len; i++){
        res.push(stack.pop()); //stack长度会不断变化
    }
    return res;
};

剑指 Offer 09. 用两个栈实现队列

https://leetcode-cn.com/leetbook/read/illustrate-lcof/xz8cid/

var CQueue = function() {
    this.stack1=[];
    this.stack2 = [];
};

/** 
 * @param {number} value
 * @return {void}
 */
CQueue.prototype.appendTail = function(value) {
    this.stack1.push(value)
};

/**
 * @return {number}
 */
CQueue.prototype.deleteHead = function() {
    if(this.stack2.length==0){
        while(this.stack1.length != 0){
            this.stack2.push(this.stack1.pop())
        }
    }
    if(this.stack2.length==0){
        return -1
    }else {
        return this.stack2.pop()
    }
};

剑指 Offer 30. 包含 min 函数的栈

https://leetcode-cn.com/leetbook/read/illustrate-lcof/xzqg03/

/**
 * initialize your data structure here.
 */
var MinStack = function() {
    this.stack1 = [];
    this.stack2 = [];
};

/**
 * @param {number} x
 * @return {void}
 */
MinStack.prototype.push = function(x) {
    this.stack1.push(x);
    if(this.stack2.length == 0 || this.stack2[this.stack2.length - 1] >= x) {
        this.stack2.push(x);
    }
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
    if(this.stack1.pop() == this.stack2[this.stack2.length - 1]) {
        this.stack2.pop();
    }
};

/**
 * @return {number}
 */
MinStack.prototype.top = function() {
    return this.stack1[this.stack1.length - 1];
};

/**
 * @return {number}
 */
MinStack.prototype.min = function() {
    return this.stack2[this.stack2.length - 1];
};

/**
 * Your MinStack object will be instantiated and called as such:
 * var obj = new MinStack()
 * obj.push(x)
 * obj.pop()
 * var param_3 = obj.top()
 * var param_4 = obj.min()
 */