[英]Find common parent-path in list of files and directories
我得到了一个文件和目录List<string> pathes
。 现在我想计算每条路径彼此共享的最深公共分支。
我们可以假设它们都有共同的路径,但这在开始时是未知的。
假设我有以下三个条目:
这应该得到结果:C:/Hello/ 因为地球正在破坏子目录的这个“链”。
第二个例子:
-> C:/Hello/World/This/Is/
你将如何进行? 我尝试使用 string.split(@"/") 并从第一个字符串开始并检查此数组的每个部分是否包含在其他字符串中。 但是,这将是一个非常昂贵的调用,因为我正在迭代 (list_of_entries)^list_of_entries。 有没有更好的解决方案?
我目前的尝试类似于以下内容(C# + LINQ):
public string CalculateCommonPath(IEnumerable<string> paths)
{
int minSlash = int.MaxValue;
string minPath = null;
foreach (var path in paths)
{
int splits = path.Split('\\').Count();
if (minSlash > splits)
{
minSlash = splits;
minPath = path;
}
}
if (minPath != null)
{
string[] splits = minPath.Split('\\');
for (int i = 0; i < minSlash; i++)
{
if (paths.Any(x => !x.StartsWith(splits[i])))
{
return i >= 0 ? splits.Take(i).ToString() : "";
}
}
}
return minPath;
}
获取最长公共前缀的函数可能如下所示:
public static string GetLongestCommonPrefix(string[] s)
{
int k = s[0].Length;
for (int i = 1; i < s.Length; i++)
{
k = Math.Min(k, s[i].Length);
for (int j = 0; j < k; j++)
if (s[i][j] != s[0][j])
{
k = j;
break;
}
}
return s[0].Substring(0, k);
}
然后你可能需要剪掉右手边的前缀。 例如,我们想返回c:/dir
而不是c:/dir/file
c:/dir/file1
c:/dir/file2
您可能还想在处理之前对路径进行规范化。 请参阅在 C# 中规范化目录名称。
我不知道这是否是性能最好的解决方案(可能不是),但它确实很容易实现。
示例代码:
List<string> paths = new List<string>();
paths.Add(@"C:/Hello/World/This/Is/An/Example/Bla.cs");
paths.Add(@"C:/Hello/World/This/Is/Not/An/Example/");
paths.Add(@"C:/Hello/Earth/Bla/Bla/Bla");
List<string> sortedPaths = paths.OrderBy(s => s).ToList();
Console.WriteLine("Most common path here: {0}", sharedSubstring(sortedPaths[0], sortedPaths[sortedPaths.Count - 1]));
当然还有那个功能:
public static string sharedSubstring(string string1, string string2)
{
string ret = string.Empty;
int index = 1;
while (string1.Substring(0, index) == string2.Substring(0, index))
{
ret = string1.Substring(0, index);
index++;
}
return ret;
} // returns an empty string if no common characters where found
首先用要检查的路径对列表进行排序。 然后您可以拆分并比较第一个和最后一个项目 - 如果它们相同,则继续下一个维度,直到找到差异为止。
所以你只需要排序一次,然后检查两个项目。
返回c:/dir
for
c:/dir/file1
c:/dir/file2
我会这样编码:
public static string GetLongestCommonPrefix(params string[] s)
{
return GetLongestCommonPrefix((ICollection<string>)s);
}
public static string GetLongestCommonPrefix(ICollection<string> paths)
{
if (paths == null || paths.Count == 0)
return null;
if (paths.Count == 1)
return paths.First();
var allSplittedPaths = paths.Select(p => p.Split('\\')).ToList();
var min = allSplittedPaths.Min(a => a.Length);
var i = 0;
for (i = 0; i < min; i++)
{
var reference = allSplittedPaths[0][i];
if (allSplittedPaths.Any(a => !string.Equals(a[i], reference, StringComparison.OrdinalIgnoreCase)))
{
break;
}
}
return string.Join("\\", allSplittedPaths[0].Take(i));
}
这里有一些测试:
[TestMethod]
public void GetLongestCommonPrefixTest()
{
var str1 = @"C:\dir\dir1\file1";
var str2 = @"C:\dir\dir1\file2";
var str3 = @"C:\dir\dir1\file3";
var str4 = @"C:\dir\dir2\file3";
var str5 = @"C:\dir\dir1\file1\file3";
var str6 = @"C:\dir\dir1\file1\file3";
var res = Utilities.GetLongestCommonPrefix(str1, str2, str3);
Assert.AreEqual(@"C:\dir\dir1", res);
var res2 = Utilities.GetLongestCommonPrefix(str1, str2, str3, str4);
Assert.AreEqual(@"C:\dir", res2);
var res3 = Utilities.GetLongestCommonPrefix(str1, str2, str3, str5);
Assert.AreEqual(@"C:\dir\dir1", res3);
var res4 = Utilities.GetLongestCommonPrefix(str5, str6);
Assert.AreEqual(@"C:\dir\dir1\file1\file3", res4);
var res5 = Utilities.GetLongestCommonPrefix(str5);
Assert.AreEqual(str5, res5);
var res6 = Utilities.GetLongestCommonPrefix();
Assert.AreEqual(null, res6);
var res7 = Utilities.GetLongestCommonPrefix(null);
Assert.AreEqual(null, res7);
}
我会迭代第一个路径中的每个字符,将它与路径集合中每个路径(第一个除外)中的每个字符进行比较:
public string FindCommonPath(List<string> paths)
{
string firstPath = paths[0];
bool same = true;
int i = 0;
string commonPath = string.Empty;
while (same && i < firstPath.Length)
{
for (int p = 1; p < paths.Count && same; p++)
{
same = firstPath[i] == paths[p][i];
}
if (same)
{
commonPath += firstPath[i];
}
i++;
}
return commonPath;
}
您可以首先遍历列表以找到最短路径,并可能稍微改进它。
为您提供最长的公共目录路径并具有最佳复杂性的函数:
private static string GetCommonPath(IEnumerable<string> files)
{
// O(N, L) = N*L; N - number of strings, L - string length
// if the first and last path from alphabetic order matches, all paths in between match
string first = null;//smallest string
string last = null;//largest string
var comparer = StringComparer.InvariantCultureIgnoreCase;
// find smallest and largest string:
foreach (var file in files.Where(p => !string.IsNullOrWhiteSpace(p)))
{
if (last == null || comparer.Compare(file, last) > 0)
{
last = file;
}
if (first == null || comparer.Compare(file, first) < 0)
{
first = file;
}
}
if (first == null)
{
// the list is empty
return string.Empty;
}
if (first.Length > last.Length)
{
// first should not be longer
var tmp = first;
first = last;
last = tmp;
}
// get minimal length
var count = first.Length;
var found = string.Empty;
const char dirChar = '\\';
var sb = new StringBuilder(count);
for (var idx = 0; idx < count; idx++)
{
var current = first[idx];
var x = char.ToLowerInvariant(current);
var y = char.ToLowerInvariant(last[idx]);
if (x != y)
{
// first and last string character is different - break
return found;
}
sb.Append(current);
if (current == dirChar)
{
// end of dir character
found = sb.ToString();
}
}
if (last.Length >= count && last[count] == dirChar)
{
// whole first is common root:
return first;
}
return found;
}
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