面试常用代码

1、单例模式——懒汉式class LazySingleton {         private static LazySingleton singleton;         private LazySingleton() {         }         public static LazySingleton getInstance() {              if (singleton == null) {                  singleton = new LazySingleton();              }              return singleton;         }     }
2、单例模式——恶汉式class HungrySingleton {         private static HungrySingleton singleton = new HungrySingleton();         private HungrySingleton() {         }         public static HungrySingleton getInstance() {              return singleton;         }     }
3、冒泡排序public static void bubbleSort(int[] arr) {         for (int i = 0; i < arr.length - 1; i++) {              boolean flag = true;// 设定一个标记，若为true，则表示此次循环没有进行交换，也就是待排序列已经有序，排序已然完成。              for (int j = 0; j < arr.length - 1 - i; j++) {                  if (arr[j] > arr[j + 1]) {                       swap(arr, j, j + 1);                       flag = false;                  }              }              if (flag) {                  break;              }         }     }
4、二叉树这块代码方面都是比较类似的就索性附上链接了！https://blog.csdn.net/android_heng/article/details/76599302
5、递归代码public int climbStairs(int n) {         int i = 1;         if (n <= 0)              return 0;         if (n == 1) {              return i;         }         if (n == 2) {              i++;              return i;         } else              return climbStairs(n - 1) + climbStairs(n - 2);     }
测试方法：public static void main(String[] args) {         ClimbStairs cs = new ClimbStairs();         int a = cs.climbStairs(4);         System.out.println(a);     }
6、快速排序      // 三数取中     // 下面的两步保证了array[hi]是最大的；     int mid=lo+(hi-lo)/2;if(array[mid]>array[hi])     {         swap(array[mid], array[hi]);     }if(array[lo]>array[hi])     {         swap(array[lo], array[hi]);     }     // 接下来只用比较array[lo]和array[mid]，让较小的在array[lo]位置就OK。     if(array[mid]>array[lo])     {         swap(array[mid], array[lo]);     }     int key = array[lo];