155.Min-Stack.md

155. Min Stack

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题目地址

https://www.lintcode.com/problem/min-stack/

https://leetcode.com/problems/min-stack/

题目描述

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.
 
Example:
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> Returns -3.
minStack.pop();
minStack.top();      --> Returns 0.
minStack.getMin();   --> Returns -2.

代码

public class Solution {
  private Stack<Integer> stack1;
  private Stack<Integer> stack2;
    public Solution () {
    stack1 = new Stack<Integer>();
    stack2 = new Stack<Integer>();
  }

  public void push(int number) {
    stack1.push(number);
    if (stack2.empty()) {
      stack2.push(number);
    } else {
      stack2.push(Math.min(number, stack2.peek()));
    }
  }

  public int pop() {
    stack2.pop();
    return stack1.pop();
  }

  public int min() {
    return stack2.peek();
  }

}