155. Min Stack

题目

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

push(x) -- Push element x onto stack. pop() -- Removes the element on top of the stack. top() -- Get the top element. getMin() -- Retrieve the minimum element in the stack.

Example:

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

题目大意

这道题是一个数据结构实现题。要求实现一个栈的类，实现 push()、pop()、top()、getMin()。

解题思路

按照题目要求实现即可。

代码

package leetcode

// MinStack define
type MinStack struct {
	elements, min []int
	l             int
}

/** initialize your data structure here. */

// Constructor155 define
func Constructor155() MinStack {
	return MinStack{make([]int, 0), make([]int, 0), 0}
}

// Push define
func (this *MinStack) Push(x int) {
	this.elements = append(this.elements, x)
	if this.l == 0 {
		this.min = append(this.min, x)
	} else {
		min := this.GetMin()
		if x < min {
			this.min = append(this.min, x)
		} else {
			this.min = append(this.min, min)
		}
	}
	this.l++
}

func (this *MinStack) Pop() {
	this.l--
	this.min = this.min[:this.l]
	this.elements = this.elements[:this.l]
}

func (this *MinStack) Top() int {
	return this.elements[this.l-1]
}

func (this *MinStack) GetMin() int {
	return this.min[this.l-1]
}

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