Leetcode_155_Min Stack

Posted 2022-11-23 皮斯特劳沃

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.

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思路：
（1）该题为实现栈的出栈、入栈等操作，返回栈的最小元素。
（2）两种实现方式。第一种方式为构建两个辅助栈；第二中方式为一个变量和一个辅助栈。本文为第二种方式，比较简单，详见代码。
（3）代码实现如下所示。希望对你有所帮助。

class MinStack 

    Stack<Integer> stack;
    int min = Integer.MAX_VALUE;

    /** initialize your data structure here. */
    public MinStack() 
        stack = new Stack<Integer>();
    

    public void push(int x) 
        if (x <= min) 

         stack.push(min);
             min = x;
        
        stack.push(x);
    

    public void pop() 
        if(stack.pop()==min) 
            min = stack.pop();            
        
    

    public int top() 
        return stack.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();
 */