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