陣列入棧出棧

class Stack{
	private Object[] data = new Object[0];	//棧的內容
	private int size = 0;	//棧的元素個數

	public boolean isFull(){	//判斷棧是否滿
		return data.length == size;
	}
	public boolean isEmpty(){	//判斷棧是否空
		return size == 0;
	}
	public void addData(){		//擴容
		data  = Array.copyOf(data,data.length+10);
	}

	public void push(Object obj){	//入棧操作
		if(isFull()){
			addData();
		}
		size++;
		data[size-1] = obj;
	}
	public Object pop(){	//出棧操作
		Object o = data[size-1];
		data[size-1] = null;
		size--;
		return o;
	}
}

public class stackTest{
	public static void main(String[] args){
		Stack s = new Stack();
		s.push(1);
		s.push("123");
		Objct o = s.pop();
		System.out.println(o);
	}
}
 

單鏈表翻轉

連結串列定義

class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
    }
}

非遞迴實現很簡單，只需要遍歷一遍連結串列，在遍歷過程中，把遍歷的節點一次插入到頭部。

public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        while(head!=null){
            ListNode tmp = head.next;
            head.next = prev;
            prev = head;
            head = tmp;
        }
        return prev;
    }
 

遞迴實現：翻轉head->為首的連結串列， 然後head變為尾部節點

public ListNode reverseList(ListNode head) {
        if(head==null||head.next ==null)
            return head;
        ListNode prev = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return prev;
    }