leetcode 算法题155 (简单036) 最小栈

• 题目介绍

设计一个支持 push，pop，top 操作，并能在常数时间内检索到最小元素的栈。

push(x) -- 将元素 x 推入栈中。
pop() -- 删除栈顶的元素。
top() -- 获取栈顶元素。
getMin() -- 检索栈中的最小元素。

• 示例

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

• 解法一

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

/** 
 * @param {number} x
 * @return {void}
 */
MinStack.prototype.push = function(x) {
  this.stack[this.stack.length] = x;
  if (this.min === null) {
    this.min = x;
  } else {
    this.min = Math.min(this.min, x);
  }
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
  if (this.stack.length) {
    let x = this.stack[this.stack.length - 1];
    this.stack.length = this.stack.length -  1;
    if (x === this.min) {
      this.setMin();
    }
  }
  return null;
};

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

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


MinStack.prototype.setMin = function() {
  let stack = this.stack;
  if (!stack.length) {
    this.min = null;
    return;
  }
  let min = stack[0], i = 1;
  while (i < stack.length) {
    min = Math.min(min, stack[i++]);
  }
  this.min = 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.getMin()
*/

执行用时 : 144ms, 在所有 JavaScript 提交中击败了95.68%的用户

内存消耗 : 44.3MB, 在所有 JavaScript 提交中击败了32.31%的用户

• 解法一

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

/** 
 * @param {number} x
 * @return {void}
 */
MinStack.prototype.push = function(x) {
  this.stack.push(x);
  if (this.min === null) {
    this.min = x;
  } else {
    this.min = Math.min(this.min, x);
  }
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
  if (this.stack.length) {
    let x = this.stack.pop();
    if (x === this.min) {
      this.setMin();
    }
  }
  return null;
};

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

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


MinStack.prototype.setMin = function() {
  let stack = this.stack;
  if (!stack.length) {
    this.min = null;
    return;
  }
  let min = stack[0], i = 1;
  while (i < stack.length) {
    min = Math.min(min, stack[i++]);
  }
  this.min = 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.getMin()
*/

执行用时 : 160ms, 在所有 JavaScript 提交中击败了75.30%的用户

内存消耗 : 44.3MB, 在所有 JavaScript 提交中击败了35.04%的用户