/**
  * 使用遞歸的二分查找
  *title:recursionBinarySearch
  *@param arr 有序數(shù)組
  *@param key 待查找關(guān)鍵字
  *@return 找到的位置
  */
 public static int recursionBinarySearch(int[] arr,int key,int low,int high){
  
  if(key < arr[low] || key > arr[high] || low > high){
   return -1;    
  }
  
  int middle = (low + high) / 2;   //初始中間位置
  if(arr[middle] > key){
   //比關(guān)鍵字大則關(guān)鍵字在左區(qū)域
   return recursionBinarySearch(arr, key, low, middle - 1);
  }else if(arr[middle] < key){
   //比關(guān)鍵字小則關(guān)鍵字在右區(qū)域
   return recursionBinarySearch(arr, key, middle + 1, high);
  }else {
   return middle;
  } 
  
 }

 /**
  * 不使用遞歸的二分查找
  *title:commonBinarySearch
  *@param arr
  *@param key
  *@return 關(guān)鍵字位置
  */
 public static int commonBinarySearch(int[] arr,int key){
  int low = 0;
  int high = arr.length - 1;
  int middle = 0;   //定義middle
  
  if(key < arr[low] || key > arr[high] || low > high){
   return -1;    
  }
  
  while(low <= high){
   middle = (low + high) / 2;
   if(arr[middle] > key){
    //比關(guān)鍵字大則關(guān)鍵字在左區(qū)域
    high = middle - 1;
   }else if(arr[middle] < key){
    //比關(guān)鍵字小則關(guān)鍵字在右區(qū)域
    low = middle + 1;
   }else{
    return middle;
   }
  }
  
  return -1;  //最后仍然沒有找到，則返回-1
 }

 public static void main(String[] args) {
 
  int[] arr = {1,3,5,7,9,11};
  int key = 4;
  //int position = recursionBinarySearch(arr,key,0,arr.length - 1);
  
  int position = commonBinarySearch(arr, key);
 
               if(position == -1){
   System.out.println("查找的是"+key+",序列中沒有該數(shù)！");
  }else{
   System.out.println("查找的是"+key+",找到位置為："+position);
  }
  
 }