LeetCode-in-All

155. Min Stack

Easy

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(int 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

import "math"

type element struct {
	Val int
	Min int
}

type MinStack struct {
	Stack []element
	Min   int
}

func Constructor() MinStack {
	return MinStack{[]element{}, math.MaxInt32}
}

func (this *MinStack) Push(val int) {
	this.Stack = append(this.Stack, element{val, this.Min})
	this.Min = min(this.Min, val)
}

func (this *MinStack) Pop() {
	l := len(this.Stack)
	this.Min = this.Stack[l-1].Min
	this.Stack = this.Stack[:l-1]
}

func (this *MinStack) Top() int {
	l := len(this.Stack)
	return this.Stack[l-1].Val
}

func (this *MinStack) GetMin() int {
	return this.Min
}

/**
 * Your MinStack object will be instantiated and called as such:
 * obj := Constructor();
 * obj.Push(val);
 * obj.Pop();
 * param_3 := obj.Top();
 * param_4 := obj.GetMin();
 */

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