剑指offer24-包含min函数的栈

包含min函数的栈

题目描述

思路

• 定义一个辅助栈

程序1

import java.util.Stack;
public class Solution {
    Stack<Integer> stack1=new Stack<Integer>();
    Stack<Integer> stack2=new Stack<Integer>();
    public void push(int node) {
        stack1.push(node);
        if(stack2.empty()){
            stack2.push(node);
        }else{
            if(stack2.peek()>=node)
                stack2.push(node);
        }
    }
    public int top() {
    return stack1.peek();
    }
    public void pop() {
        if(stack1.peek()==stack2.peek())
            stack2.pop();
        stack1.pop();
    }
    
    public int min() {
        return stack2.peek();
    }
}

程序2

• 牛客

import java.util.Stack;
import java.util.Arrays;
public class Solution {
/*借用辅助栈存储min的大小，自定义了栈结构
*/
    private int size;
    private int min = Integer.MAX_VALUE;
    private Stack<Integer> minStack = new Stack<Integer>();
    private Integer[] elements = new Integer[10];
    public void push(int node) {
        ensureCapacity(size+1);
        elements[size++] = node;
        if(node <= min){
            minStack.push(node);
            min = minStack.peek();
        }else{
            minStack.push(min);
        }
    //    System.out.println(min+"");
    }
 
    private void ensureCapacity(int size) {
        // TODO Auto-generated method stub
        int len = elements.length;
        if(size > len){
            int newLen = (len*3)/2+1; //每次扩容方式
            elements = Arrays.copyOf(elements, newLen);
        }
    }
    public void pop() {
        Integer top = top();
        if(top != null){
            elements[size-1] = (Integer) null;
        }
        size--;
        minStack.pop();    
        min = minStack.peek();
    //    System.out.println(min+"");
    }
 
    public int top() {
        if(!empty()){
            if(size-1>=0)
                return elements[size-1];
        }
        return (Integer) null;
    }
    public boolean empty(){
        return size == 0;
    }
 
    public int min() {
        return min;
    }
}