从文件系统中删除子目录

给定一个字符串数组arr [] ，该字符串数组由N个唯一的目录组成，形式为字符串，任务是删除所有子目录并打印最终数组。

A directory S is a subdirectory if there exists any directory D such that S is the prefix of D.

例子：

Input: arr[] = {“/a”, “/a/j”, “/c/d/e”, “/c/d”, “/b”}
Output: { “/a”, “/c/d”, “/b”}
Explanation: Directory “/a/j” is a subdirectory of directory “/a”, and “/c/d/e” is a subdirectory of directory “/c/d”.
Therefore, remove both of them.

Input: arr[] = {“/a”, “/a/b”, “/a/b/c”, “/a/b/c/d”}
Output: {“/a”}
Explanation: All directories are subdirectories of “/a”

天真的方法：最简单的方法是遍历数组以检查每个字符串(如果存在以它为前缀的字符串) ，然后从数组中删除此类字符串。

时间复杂度： O(len * N ² ) ，其中len是数组中最长字符串的长度。
辅助空间： O(N)

高效的方法：想法是对给定的数组进行排序，并将位置i的当前目录与索引(i -1)的先前目录进行比较。如果arr [i – 1]是arr [i]的前缀，则删除arr [i] 。检查整个阵列后，打印其余目录。请按照以下步骤解决问题：

• 按字母顺序对所有目录进行排序，并初始化向量res 。
• 将第一个目录插入res 。
• 用最后一个有效目录(即res的最后一个目录)检查每个目录。
• 如果该目录等于先前有效目录的某个前缀，则该目录无效(子目录)。否则它是有效的。
• 如果当前目录有效，则将其添加到res 。
• 完成遍历后，打印出res中存在的所有目录。

下面是上述方法的实现：

C++

// C++ program for the above approach
 
#include 
using namespace std;
 
// Function to remove sub-directories
// from the given lists dir
void eraseSubdirectory(vector& dir)
{
    // Store final result
    vector res;
 
    // Sort the given directories
    sort(dir.begin(), dir.end());
 
    // Insert 1st directory
    res.push_back(dir[0]);
 
    cout << "{" << dir[0] << ", ";
 
    // Iterating in directory
    for (int i = 1; i < dir.size(); i++) {
 
        // Current directory
        string curr = dir[i];
 
        // Our previous valid directory
        string prev = res.back();
 
        // Find length of previous directory
        int l = prev.length();
 
        // If subdirectory is found
        if (curr.length() > l && curr[l] == '/'
            && prev == curr.substr(0, l))
            continue;
 
        // Else store it in result
        // valid directory
        res.push_back(curr);
 
        cout << curr << ", ";
    }
 
    cout << "}\n";
}
 
// Driver Code
int main()
{
    // Given lists of directories dir[]
    vector dir
        = { "/a", "/a/j", "/c/d/e",
            "/c/d", "/b" };
 
    // Function Calll
    eraseSubdirectory(dir);
 
    return 0;
}

Java

// Java program for the above approach
import java.io.*;
import java.util.*;
 
class GFG{
 
// Function to remove sub-directories
// from the given lists dir
static void eraseSubdirectory(ArrayList dir)
{
     
    // Store final result
    ArrayList res = new ArrayList();
 
    // Sort the given directories
    Collections.sort(dir);
 
    // Insert 1st directory
    res.add(dir.get(0));
 
    System.out.print("{" + dir.get(0) + ", ");
 
    // Iterating in directory
    for(int i = 1; i < dir.size(); i++)
    {
         
        // Current directory
        String curr = dir.get(i);
 
        // Our previous valid directory
        String prev = res.get(res.size() - 1);
 
        // Find length of previous directory
        int l = prev.length();
 
        // If subdirectory is found
        if (curr.length() > l &&
           curr.charAt(l) == '/' &&
           prev.equals(curr.substring(0, l)))
            continue;
 
        // Else store it in result
        // valid directory
        res.add(curr);
 
        System.out.print(curr + ", ");
    }
    System.out.print("}\n");
}
 
// Driver Code
public static void main(String[] args)
{
     
    // Given lists of directories dir[]
    ArrayList dir = new ArrayList(Arrays.asList(
            "/a", "/a/j", "/c/d/e", "/c/d", "/b"));
 
    // Function Call
    eraseSubdirectory(dir);
}
}
 
// This code is contributed by akhilsaini

Python3

# Python3 program for the above approach
 
# Function to remove sub-directories
# from the given lists dir
def eraseSubdirectory(dir):
     
    # Store final result
    res = []
 
    # Sort the given directories
    dir.sort()
 
    # Insert 1st directory
    res.append(dir[0])
 
    print("{", dir[0], end = ", ")
 
    # Iterating in directory
    for i in range(1, len(dir)):
         
        # Current directory
        curr = dir[i]
 
        # Our previous valid directory
        prev = res[len(res) - 1]
 
        # Find length of previous directory
        l = len(prev)
 
        # If subdirectory is found
        if (len(curr) > l and
           curr[l] == '/' and
              prev == curr[:l]):
            continue
 
        # Else store it in result
        # valid directory
        res.append(curr)
        print(curr, end = ", ")
 
    print("}")
 
# Driver Code
if __name__ == '__main__':
 
    # Given lists of directories dir[]
    dir = [ "/a", "/a/j", "/c/d/e", "/c/d", "/b" ]
 
    # Function Call
    eraseSubdirectory(dir)
 
# This code is contributed by akhilsaini

C#

// C# program for the above approach
using System;
using System.Collections;
 
class GFG{
 
// Function to remove sub-directories
// from the given lists dir
static void eraseSubdirectory(ArrayList dir)
{
     
    // Store final result
    ArrayList res = new ArrayList();
 
    // Sort the given directories
    dir.Sort();
 
    // Insert 1st directory
    res.Add(dir[0]);
 
    Console.Write("{" + dir[0] + ", ");
 
    // Iterating in directory
    for(int i = 1; i < dir.Count; i++)
    {
         
        // Current directory
        string curr = (string)dir[i];
 
        // Our previous valid directory
        string prev = (string)res[(res.Count - 1)];
 
        // Find length of previous directory
        int l = prev.Length;
 
        // If subdirectory is found
        if (curr.Length > l && curr[l] == '/' &&
            prev.Equals(curr.Substring(0, l)))
            continue;
 
        // Else store it in result
        // valid directory
        res.Add(curr);
 
        Console.Write(curr + ", ");
    }
    Console.Write("}\n");
}
 
// Driver Code
public static void Main()
{
     
    // Given lists of directories dir[]
    ArrayList dir = new ArrayList(){ "/a", "/a/j",
                                     "/c/d/e",
                                     "/c/d", "/b" };
 
    // Function Call
    eraseSubdirectory(dir);
}
}
 
// This code is contributed by akhilsaini

输出：

{/a, /b, /c/d, }

时间复杂度： O(N * log N)
辅助空间： O(N)