面试算法——2.双栈实现队列

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import java.util.Stack;public class Pro_1_GetMinStack {//stackData :当前序列入栈private Stack<Integer> stackData;//stackMin : 栈顶为当前序列的最小private Stack<Integer> stackMin;public Pro_1_GetMinStack(){stackData = new Stack<>();stackMin = new Stack<>();}/** 对数num* stackData 正常入栈 push(num)* * stackMin 为空 则 push(num);* 非空 则将stackMIn 栈顶与num比较，num更小则入stackMin栈，否则不处理* * */public void push(int num){if(stackMin.isEmpty()){stackMin.push(num);}else if(num<=stackMin.peek()){stackMin.push(num);}stackData.push(num);}/** 出栈stackData，为空则报异常* 否则正常出栈，值保存为value* * stackMin栈顶与value比较，只有相等和小于value两种情况，等于时，出栈;* 否则不处理* * 如何进栈，就如何出栈* */public int pop(){if(stackData.isEmpty()){throw new RuntimeException("your stack is empty.");}int value = stackData.pop();if(value==stackMin.peek()){stackMin.pop();}return value;}//获取stackMin的栈顶，注意为空时，抛异常public int getmin(){if(stackMin.isEmpty()){throw new RuntimeException("your stack is empty.");}return stackMin.peek();}//test public static void main(String[] args) {// TODO Auto-generated method stubPro_1_GetMinStack stack1=new Pro_1_GetMinStack();stack1.push(3);System.out.println(stack1.getmin());stack1.push(4);System.out.println(stack1.getmin());stack1.push(1);System.out.println(stack1.getmin());System.out.println(stack1.pop());System.out.println(stack1.getmin());}}
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