二分查找之算法

/**
 * arr：数组
 * key：关键字
 * mid：关键字的下标
 * low：数组第一个数的下标
 * high：数组最后一个数的下标
 */
function bsFdg(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;
    }
  }
  return -1;
}
console.log(bsFdg([3,6,9,16,18],16));

function bsDg(arr, low, high, key) {
  if(low > high) return -1;
  var mid = parseInt((low + high)/2);
  if(key == arr[mid]) {
    return mid;
  } else if(key > arr[mid]) {
    return bsDg(arr, mid+1, high, key);
  } else if(key < arr[mid]) {
    return bsDg(arr, low, mid-1, key);
  }
}
console.log(bsDg([3,6,9,15,17],0,4,17));