4. ＜tag-栈和排序问题＞-面试题 03.05. 栈排序 + 面试真题: 对栈进行排序

面试题 03.05. 栈排序

[案例需求]

[思路分析]

[代码实现]

class SortedStack {
    
    Deque<Integer> sortedStack = new LinkedList<>();
    Deque<Integer> tempStack = new LinkedList<>();
    public SortedStack() {

    }
    
    public void push(int val) {
        //辅助栈为空, 直接插入到主栈
        //辅助栈不为空, 比较后, 把较小的放入辅助栈, 较大的放入主栈(持续的过程!)

        if(sortedStack.isEmpty()){
            sortedStack.push(val);
        }else{
            while(sortedStack.peek() < val){
                tempStack.push(sortedStack.pop());

                if(isEmpty())break;
            }

            sortedStack.push(val);

            while(! tempStack.isEmpty()){
                sortedStack.push(tempStack.pop());
            }
        }
        

    }
    
    public void pop() {
        if(!isEmpty())sortedStack.pop();
    }
    
    public int peek() {
        if(!isEmpty()){
            return sortedStack.peek();
        }else{
            return -1;
        }
    }
    
    public boolean isEmpty() {
        return sortedStack.isEmpty();
    }
}

/**
 * Your SortedStack object will be instantiated and called as such:
 * SortedStack obj = new SortedStack();
 * obj.push(val);
 * obj.pop();
 * int param_3 = obj.peek();
 * boolean param_4 = obj.isEmpty();
 */

面试真题: 对栈进行排序

[案例需求]

[思路分析]

[代码实现]

import java.util.*;

public class test {
    public static void main(String[] args) {

        //双栈排序int temp = 0;
        Stack<Integer> st = new Stack();
        st.push(4);
        st.push(2);
        st.push(1);
        st.push(3);

        //排序过程. 建立辅助栈, 把主栈出栈一个元素放入辅助栈, 比较主栈栈顶, 1 < 3, 把1出栈, 把3出栈主栈, 1入栈到辅助栈,
        Deque<Integer> stack = new LinkedList<>();
        if(st.isEmpty())stack.push(st.pop());

        //比较主栈和辅助栈的栈顶;
        int temp = 0;
        while(!st.isEmpty()){
            temp = st.pop();

            if(stack.isEmpty() || temp > stack.peek()){
                stack.push(temp);
            }else{
                st.push(stack.pop());
                stack.push(temp);
            }
        }

        //遍历stack
        while(!stack.isEmpty()){
            System.out.println(stack.pop());
        }
    }
}