Jianzhi offer 09. realize queue with two stacks

Knowledge points used ： Create a stack , Judge whether the stack is empty , Stack pop and push

1. Create a stack

 Take integer as an example 
Stack<Integer> st;
st = new Stack<n>();

 Analogy base type 
int a;
a=5;

Stack<Integer> st;

Stack Indicates that the declared container is a stack

Intege Indicates that the variables stored in the stack are of integer type

st Is the name of the stack

st = new Stack<n>();

new Create objects

<n> When n For a specific number of hours , Such as 5, Indicates that the stack can store at most 5 A variable

        When n It's empty time , Indicates that the stack can be stored casually , as follows

st = new Stack<>()

2. Stack function

Yes empty(),pop(),push()

empty()  Test if the stack is empty , return boolean
st.empty();

pop()     Out of the stack , Return the value of the element out of the stack 
a = st.pop();

push(a)   take a Push 
st.push(a)

Some other functions

peek()     Look at the top element of the stack , But don't remove it 

search(a)     return a Position in the stack , With 1 Cardinal number 

3. Solution code

class CQueue {
    // queue ： fifo 
        // Declare two stacks 
    private Stack<Integer> st1;
    private Stack<Integer> st2;
    public CQueue() {
        st1=new Stack<>();// fixed collocation  Stack<Interger> name=Stace<>()
        st2=new Stack<>();
    }
    
    public void appendTail(int value) {
        
        // Judge whether the first pair of columns is empty , If it's empty, put it directly 
        // If it is not empty, move all the data to 2, Put it in and move it back 
        // use while loop , Put it all directly 2
        while(!st1.empty())
        {
            st2.push(st1.pop());
        }
        st1.push(value);
        while(!st2.empty())
        {
            st1.push(st2.pop());
        }
    }
    
    public int deleteHead() {
        // Judge 1 Is it empty 
        // Empty null
        // It's not empty pop
        if(st1.empty())
        {
            return -1;
        }
        else
        {
            return st1.pop();
        }
    }
}

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue obj = new CQueue();
 * obj.appendTail(value);
 * int param_2 = obj.deleteHead();
 */