public class BinarySearch {
  /**
   * 二分查找算法
   * 
   * @param srcArray
   *      有序數(shù)組
   * @param key
   *      查找元素
   * @return key的數(shù)組下標，沒找到返回-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));
  }
 
  // 二分查找遞歸實現(xiàn)
  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;
  }
 
  // 二分查找普通循環(huán)實現(xiàn)
  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;
  }
}