冒泡排序

        for(int i =0;i<arr.length-1;i++) {
            for(int j=0;j<arr.length-i-1;j++) {//-1为了防止溢出
                if(arr[j]>arr[j+1]) {
                    int temp = arr[j];

                    arr[j]=arr[j+1];

                    arr[j+1]=temp;
                }
            }
        }
    }

二分查找法

给定数组是按从小到大排序好的

        //先排序
        bubbleSort(arr);
        int left = 0;
        int right = arr.length - 1;
        int mid;
        while(left <= right){
            mid = (left + right) % 2 == 0 ? (left + right) / 2 : (left + right) / 2 + 1;
            if(arr[mid] > val){
                right = mid  ;
            }else if (arr[mid] < val){
                left = mid ;
            }else{
                //找到该值
             **   System.out.println(mid);**
                return;
            }
        }

    }

单链表反转

public class SingleLinkedList{

      private static class Node{
          private int val;
          private Node next;  
      }

      //递归反转1-2-3-4
      public Node reverse1(Node node){
          if(node.next ==null || node== null){
            return node;
          }
          Node temp= node.next;
          Node newNode = reverse1(node.next);
          node.next = null;
          temp.next = node;
          return newNode;
       }
  
    //遍历1-2-3-4
    public Node reverse2(Node head){
       Node prev = null;
       Node next = null;
       while (head != null){
           next =  head.next;
           head.next = prev;  //在这里完成4->3->2->1
           prev = head;
           head = next;
       }
       return prev;
    }
}