栈与队列-包含 min 函数的栈

剑指 Offer 30. 包含 min 函数的栈

定义栈的数据结构，请在该类型中实现一个能够得到栈的最小元素的 min 函数在该栈中，调用 min、push 及 pop 的时间复杂度都是 O(1)。

示例:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.min();   --> 返回 -3.
minStack.pop();
minStack.top();      --> 返回 0.
minStack.min();   --> 返回 -2.

题解 1:

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

/** 
 * @param {number} x
 * @return {void}
 */
MinStack.prototype.push = function(x) {
    this.stack.push(x)
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
    this.stack.pop()
};

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

/**
 * @return {number}
 */
MinStack.prototype.min = function() {
    let min = this.stack[0];
    //时间复杂度O(N)
    for(let value of this.stack){
        if(value < min){
            min = value
        }
    }
    return min
};

/**
 * 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()
 */

题解 2:

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

/** 
 * @param {number} x
 * @return {void}
 */
MinStack.prototype.push = function(x) {
    this.stack.push(x);
    //为空时添加一个并且结束
    if(!this.minStack.length){
        this.minStack.push(x)
        return
    }
    const minLastData = this.minStack[this.minStack.length - 1];
    if( minLastData > x){
        this.minStack.push(x)
    }else{
        this.minStack.push(minLastData)
    }
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
    this.stack.pop()
    this.minStack.pop()
};

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

/**
 * @return {number}
 */
MinStack.prototype.min = function() {
    return this.minStack[this.minStack.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()
 */

规则:

题解1 -> 牺牲时间O(N)换空间 题解2 -> 使用空间O(N)换取时间O(1)

题目来源：leetcode