155.最小栈.md

155. 最小栈

url

题目

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。

输入：
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]
输出：
[null,null,null,null,-3,null,0,-2]
解释：
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.

方法

双栈即可

• 数据栈与最小栈

code

js

let MinStack = function() {
    this.dataStack = [];
    this.minStack = [];
    this.min = Infinity;
}
MinStack.prototype.push = function(x) {
    this.dataStack.push(x);
    this.min = Math.min(this.min, x);
    this.minStack.push(this.min);
}
MinStack.prototype.pop = function() {
    this.dataStack.pop();
    this.minStack.pop();
    this.min = this.minStack.length === 0 ? Infinity : this.minStack[this.minStack.length - 1];
}
MinStack.prototype.top = function()  {
    return this.dataStack[this.dataStack.length - 1];
}
MinStack.prototype.getMin = function() {
    return this.min;
}
var test = new MinStack();
test.push(2);
test.push(1);
test.push(3);
// test.pop();
console.log(test.getMin());
console.log(test.top());

go

const (
	INT_MAX = int(^uint((0)) >> 1)
	INT_MIN = ^INT_MAX
)
var min = INT_MAX
var s1 = []int{}
var s2 = []int{}
func push(x int) {
	s1 = append(s1, x)
	min = Min(min, x)
	s2 = append(s2, min)
}
func pop() {
	s1 = s1[:len(s1) - 1]
	s2 = s2[:len(s2) - 1]
	if len(s2) == 0 {
		min = INT_MAX
	} else {
		min = s2[len(s2) - 1]
	}
}
func top() int {
	return s1[len(s1) - 1]
}
func getMin() int {
	return min
}

java

class MinStack {
    private Stack<Integer> dataStack;
    private Stack<Integer> minStack;
    private int min;
    /** initialize your data structure here. */
    public MinStack() {
        dataStack = new Stack<>();
        minStack = new Stack<>();
        min = Integer.MAX_VALUE;
    }
    public void push(int x) {
        dataStack.push(x);
        min = Math.min(min, x);
        minStack.push(min);
    }
    public void pop() {
        dataStack.pop();
        minStack.pop();
        min = minStack.isEmpty() ? Integer.MAX_VALUE : minStack.peek();
    }
    public int top() {
        return dataStack.peek();
    }
    public int getMin() {
        return min;
    }
}
/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */