LeetCode--155--最小栈(java版)

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。

示例:

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.

class MinStack {
    private Stack<Integer> stack1;
    private Stack<Integer> stack2;
    /** initialize your data structure here. */
    public  MinStack() {
        this.stack1 = new Stack<Integer>();
        this.stack2 = new Stack<Integer>();
    }
    
    public void push(int x) {
        this.stack1.push(x);
        if(this.stack2.isEmpty()){
            this.stack2.push(x);
        }else if(x < this.stack2.peek()){
            this.stack2.push(x);
        }else{
            this.stack2.push(stack2.peek());
        }
    }
    
    public void pop() {
            this.stack1.pop();
            this.stack2.pop(); 
    }
    
    public int top() {
            return this.stack1.peek();
    }
    
    public int getMin() {
        return this.stack2.peek();
        }
    }

/**
 * 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();
 */

2019-03-03 16:21:27