二进制搜索已排序的数组

我正在尝试使用此二进制搜索代码搜索降序排序数组。 然而，在我对它进行排序并尝试搜索之后，它不会带来任何结果，只是一个永远不会消失的加载图标，就像它有一个无限循环一样。 我不确定问题是什么，因为代码看起来合乎逻辑。

这是带有4.0框架的aspx，c＃。 提前致谢！

protected void Button2_Click(object sender, EventArgs e) { String item = TextBox1.Text; int target = Convert.ToInt16(item); int mid, first = 0, last = mynumbers.Length - 1; //for a sorted array with descending values while (first<=last) { mid = (first + last) / 2; if (target  mynumbers[mid]) last = mid - 1; else Label11.Text = "Target " + item + " was found at index " + mynumbers[mid]; } 

Answer 1

Array类中有二进制搜索：

 int index = Array.BinarySearch(mynumbers, target); 

对于降序，可以使用ReverseComparer轻松完成，这很容易编写，如：

  public class ReverseComparer : IComparer { public int Compare(T x, T y) { return Comparer.Default.Compare(y, x); } } 

然后：

 int index = Array.BinarySearch(numbers, 7, new ReverseComparer()); 

如果这是学术练习，您必须使用自定义搜索，当然，这不适用。 如果它必须是一个类的自定义算法，那么问题是你必须在找到时突破循环，并且索引处于mid ，而不是mynumbers[mid] ：

  //for a sorted array with descending values while (first<=last) { mid = (first + last) / 2; if (target < mynumbers[mid]) { first = mid + 1; } if (target > mynumbers[mid]) { last = mid - 1; } else { // the index is mid, not mynumbers[mid], and you need to break here // once found or it's an infinite loop once it finds it. Label11.Text = "Target " + item + " was found at index " + mid; break; } } 

实际上，我可能会设置一个bool标志来保持算法的纯净，而不是将find与输出问题混合在一起，这也可以让你更容易分辨出如果你没有找到它就退出循环：

  bool found = false; //for a sorted array with descending values while (!found && first<=last) { mid = (first + last) / 2; if (target < mynumbers[mid]) { first = mid + 1; } if (target > mynumbers[mid]) { last = mid - 1; } else { // You need to stop here once found or it's an infinite loop once it finds it. found = true; } } Label11.Text = found ? "Item " + item + " was found at position " + mid : "Item " + item + " was not found"; 

Answer 2

在黑暗中拍摄：

 if (target < mynumbers[mid]) first = mid + 1; else if (target > mynumbers[mid]) last = mid - 1; else { .... break; } 

我怀疑你在中午1点到1点中间来回蹦蹦跳跳

Answer 3

这是正确的：

如果target< mynumbers[mid]那么你必须采取最后一次到中期1，因为我们必须搜索较低的范围，即从第一个到第一个中期

 while (first<=last) { mid = (first + last) / 2; if (target == mynumbers[mid]) Label11.Text = "Target " + item + " was found at index " + mynumbers[mid]; else if (target < mynumbers[mid]) last = mid - 1; else (target > mynumbers[mid]) first = mid + 1; } 

Answer 4

 //this works fine with these Test cases // has to check if (target == mynumbers[mid]) // this is for an array with ascending order. class Program { static void Main(string[] args) { // TEST cases: // for 8: item 8 was not found // for 4: item 4 found at Position 3 // for 1: item 1 found at position 0 // for 0: item 0 was not found int target =8; int searchkey = target; int[] mynumbers = { 1, 2, 3, 4, 5 }; int mid=0, first = 0, last = mynumbers.Length - 1; bool found = false; //for a sorted array with ascending values while (!found && first <= last) { mid = (first + last) / 2; if (target == mynumbers[mid]) found = true; else { if (target > mynumbers[mid]) { first = mid + 1; } if (target < mynumbers[mid]) { last = mid - 1; } } } String foundmsg = found ? "Item " + searchkey + " was found at position " + mid : "Item " + searchkey + " was not found"; Console.WriteLine(foundmsg); } } 

Answer 5

它对我有用

 public static int search(int[] arr, int value) { Debug.Assert(arr.Length>0); var left = 0; var right = arr.Length - 1; while (((right - left)/2) > 0) { var middle = left + (right - left)/2; if (arr[middle] < value) left = middle + 1; else right = middle; } return arr[left] >= value ? left : right; } 

Answer 6

  int num = 2; int[] value = { 1, 2, 3, 4, 5, 6,7,8,9,10,11,12,13,14,15,16,17,18,19,20 }; int s = 0; int e = value.Length - 1; int m = (s + e) / 2; bool find = false; do { if (value[m] == num) { Console.WriteLine("We have found the given number"); find = true; } else if (num < value[m]) { e = m - 1; } else { s = m + 1; } m = (s + e) / 2; } while (find != true); 

Answer 7

 public static object BinnarySearch(int[] array,int SearchKey) { int min = 0; int max = array.Length - 1; while (min <= max) { int mid = (min + max) / 2; if (SearchKey == array[mid]) { return mid; } else if (SearchKey < array[mid]) { max = mid - 1; } else min = mid + 1; } return "Not Found"; }