LeetCode Notes: Min Stack

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Question

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Implement the MinStack class:

  • MinStack() initializes the stack object.
  • void push(val) pushes the element val onto the stack.
  • void pop() removes the element on the top of the stack.
  • int top() gets the top element of the stack.
  • int getMin() retrieves the minimum element in the stack.

Example 1:

Input

["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]

Output

[null,null,null,null,-3,null,0,-2]

Explanation

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

Constraints:

  • -231 <= val <= 231 - 1
  • Methods pop, top and getMin operations will always be called on non-empty stacks.
  • At most 3 * 104 calls will be made to push, pop, top, and getMin.

Solution

Analysis:

Use the array feature of javascript to operate, use the array to simulate a stack

Code:

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

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

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
    //Delete the last element
    this.stack.splice(this.stack.length-1,1)
};

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

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

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

Reference

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