查找

 function 二分查找(arr, key) {
    var low = 0,
     high = arr.length - 1;
    while(low <= high){
     var mid = parseInt((high + low) / 2);
     if(key == arr[mid]){
      return mid;
     }else if(key > arr[mid]){
      low = mid + 1;
     }else if(key < arr[mid]){
      high = mid -1;
     }else{
      return -1;
     }
    }
   };
   var arr = [1,2,3,4,5,6,7,8,9,10,11,23,44,86];
   var result = 二分查找(arr,10);
   alert(result); // 9 返回目标元素的索引值  
   
  // 递归算法
   function 二分查找(arr,low, high, key) {
    if (low > high){
     return -1;
    }
    var mid = parseInt((high + low) / 2);
    if(arr[mid] == key){
     return mid;
    }else if (arr[mid] > key){
     high = mid - 1;
     return 二分查找(arr, low, high, key);
    }else if (arr[mid] < key){
     low = mid + 1;
     return 二分查找(arr, low, high, key);
    }
   };
   var arr = [1,2,3,4,5,6,7,8,9,10,11,23,44,86];
   var result = 二分查找(arr, 0, 13, 10);
   alert(result); // 9 返回目标元素的索引值