两个栈实现一个队列

 

 两个栈实现一个队列

思路:所有元素进stack1，然后全部出stack1并进入stack2.实现队列的先进先出即：若stack2非空，我们需要的恰好再栈顶，出栈;

若要给队列添加元素，即先进sack1,要出队时，若stack2不为空就出栈，为空时就把stack1全部进栈到stack2

 

 

package lianggezhanshixianyigeduilie;

class Stack{
    int top;
    int[]elem;
    public Stack(){
        this(10);
    }
    public Stack(int size){
        this.elem=new int[size];
        this.top=0;
    }
    public boolean isFull(){
        if(this.top==this.elem.length){
            return true;
        }
        return false;
    }
    public boolean push(int val){
        if(isFull()){
            return false;            
        }
        this.elem[this.top++]=val;
        return true;
    }
    public boolean isEmpty(){
        if(this.top==0){
            return true;            
        }
        return false;
    }
    public int pop(){
        if(isEmpty()){
            return -1;            
        }
        --this.top;
        
        return this.elem[this.top];
    }
    
    
}

public class Solution1 {
    
    Stack stack1=new Stack(); 
    Stack stack2=new Stack(); 
    public void insertTail(int x){//添加元素到队尾 --进队--- 
        stack1.push(x); 
        } 
    public boolean isEmpty1(){
        if(stack1.top==0&&stack2.top==0){
            return true;            
        }
        return false;
    }
    public int pop1(){//删除队首 --出队--- 必须是队不为空才能删除
                      if( !isEmpty1()){//队列不为空          
                          if(stack2.isEmpty()){//若stack2为空，则把stack1全部加入stack2 
                              stack1ToStack2();
                          }
                          return stack2.pop(); 
                      }else{ 
                              System.out.println("队列已经为空，不能执行从队头出队");
                              return -1; 
                              }     
                      }      
    public void stack1ToStack2(){//把stack1全部放入stack2      
            while(!stack1.isEmpty()){
                stack2.push(stack1.pop());
            }     
        }
    
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Solution1 q=new Solution1 (); 
        q.insertTail(1);
        q.insertTail(2); 
        q.insertTail(3); 
        q.insertTail(4); 
        System.out.println(q.pop1());
        System.out.println(q.pop1()); 
        q.insertTail(5); 
        System.out.println(q.pop1());
        System.out.println(q.pop1()); 
        System.out.println(q.pop1()); 
        System.out.println(q.pop1()); 
        
    }

}