Java实现冒泡排序、折半查找

1、冒泡排序

public class BubbleSort{
      public static void main(String[] args){
          int score[] = {67, 69, 75, 87, 89, 90, 99, 100};
          for (int i = 0; i < score.length -1; i++){    //最多做n-1趟排序
              for(int j = 0 ;j < score.length - i - 1; j++){    //对当前无序区间score[0......length-i-1]进行排序(j的范围很关键，这个范围是在逐步缩小的)
                  if(score[j] < score[j + 1]){    //把小的值交换到后面
                      int temp = score[j];
                      score[j] = score[j + 1];
                      score[j + 1] = temp;
                  }
              }
              System.out.print("第" + (i + 1) + "次排序结果：");
              for(int a = 0; a < score.length; a++){
                  System.out.print(score[a] + "\t");
              }
              System.out.println("");
          }
              System.out.print("最终排序结果：");
              for(int a = 0; a < score.length; a++){
                  System.out.print(score[a] + "\t");
         }
      }
  } 

2、折半查找

public class BinarySearch {
    /**
    * 二分查找算法
    *
    * @param srcArray 有序数组
    * @param key 查找元素
    * @return key的数组下标，没找到返回-1
    */
    public static void main(String[] args) {
        int srcArray[] = {3,5,11,17,21,23,28,30,32,50,64,78,81,95,101};
        System.out.println(binSearch(srcArray, 0, srcArray.length - 1, 81));
    } 

    // 二分查找递归实现
    public static int binSearch(int srcArray[], int start, int end, int key) {
        int mid = (end - start) / 2 + start;
        if (srcArray[mid] == key) {
            return mid;
        }
        if (start >= end) {
            return -1;
        } else if (key > srcArray[mid]) {
            return binSearch(srcArray, mid + 1, end, key);
        } else if (key < srcArray[mid]) {
            return binSearch(srcArray, start, mid - 1, key);
        }
        return -1;
    } 

    // 二分查找普通循环实现
    public static int binSearch(int srcArray[], int key) {
        int mid = srcArray.length / 2;
        if (key == srcArray[mid]) {
            return mid;
        }   

        int start = 0;
        int end = srcArray.length - 1;
        while (start <= end) {
            mid = (end - start) / 2 + start;
            if (key < srcArray[mid]) {
               end = mid - 1;
            } else if (key > srcArray[mid]) {
                start = mid + 1;
            } else {
                return mid;
            }
        }
        return -1;
    }
} 

计算中间位置使用：

int mid = (end - start) / 2 + start;

防止加法运算时可能导致的整数越界