递归

递归求和

public class Sum {
    public static  int sum(int [] arr)
    {
       return sum(arr,0);
    }

    private  static  int sum(int [] arr,int index)
    {
        if(index==arr.length)
        {
            return  0;
        }
        return  arr[index]+sum(arr,index+1);
    }

    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 4, 5, 6, 7, 8};
        System.out.println(sum(nums));
    }
}

链表删除元素递归实现

public class Solution4 {
    public ListNode removeElements(ListNode head, int val) {
        if (head == null) {
            return head;
        }
        ListNode res = removeElements(head.next, val);
        if (head.val == val) {
            return res;
        } else {
            head.next = res;
            return head;
        }
    }
    public static void main(String[] args) {

        int[] nums = {1, 2, 6, 3, 4, 5, 6};
        ListNode head = new ListNode(nums);
        System.out.println(head);

        ListNode res = (new Solution4()).removeElements(head, 6);
        System.out.println(res);
    }
}

运行机制