前缀与给定字符串匹配到给定长度k的字符串计数

给定字符串数组arr []并给定一些查询，其中每个查询均由字符串str和整数k组成。任务是在arr []中找到字符串计数，其长度为k的前缀与k的长度str匹配。

例子：

Input: arr[] = {“abba”, “abbb”, “abbc”, “abbd”, “abaa”, “abca”}, str = “abbg”, k = 3
Output: 4
“abba”, “abbb”, “abbc” and “abbd” are the matching strings.

Input: arr[] = {“geeks”, “geeksforgeeks”, “forgeeks”}, str = “geeks”, k = 2
Output: 2

先决条件： Trie | (插入和搜索)

方法：我们将形成一个trie并将所有字符串插入该trie中，并为每个节点创建另一个变量(频率)，该变量将存储给定字符串的前缀频率。现在要获取其前缀与给定字符串匹配到给定长度k的字符串的计数，我们必须从根开始遍历trie到长度k，Node的频率将给出此类字符串的计数。

下面是上述方法的实现：

C++

// C++ implementation of the approach
#include 
using namespace std;
  
// Trie node (considering only lowercase alphabets)
struct Node {
    Node* arr[26];
    int freq;
};
  
// Function to insert a node in the trie
Node* insert(string s, Node* root)
{
    int in;
    Node* cur = root;
    for (int i = 0; i < s.length(); i++) {
        in = s[i] - 'a';
  
        // If there is no node created then create one
        if (cur->arr[in] == NULL)
            cur->arr[in] = new Node();
  
        // Increase the frequency of the node
        cur->arr[in]->freq++;
  
        // Move to the next node
        cur = cur->arr[in];
    }
  
    // Return the updated root
    return root;
}
  
// Function to return the count of strings
// whose prefix of length k matches with the
// k length prefix of the given string
int find(string s, int k, Node* root)
{
    int in, count = 0;
    Node* cur = root;
  
    // Traverse the string
    for (int i = 0; i < s.length(); i++) {
        in = s[i] - 'a';
  
        // If there is no node then return 0
        if (cur->arr[in] == NULL)
            return 0;
  
        // Else traverse to the required node
        cur = cur->arr[in];
  
        count++;
  
        // Return the required count
        if (count == k)
            return cur->freq;
    }
    return 0;
}
  
// Driver code
int main()
{
    string arr[] = { "abba", "abbb", "abbc", "abbd", "abaa", "abca" };
    int n = sizeof(arr) / sizeof(string);
  
    Node* root = new Node();
  
    // Insert the strings in the trie
    for (int i = 0; i < n; i++)
        root = insert(arr[i], root);
  
    // Query 1
    cout << find("abbg", 3, root) << endl;
  
    // Query 2
    cout << find("abg", 2, root) << endl;
  
    // Query 3
    cout << find("xyz", 2, root) << endl;
  
    return 0;
}

Java

// Java implementation of the approach
class GFG 
{
  
    // Trie node (considering only lowercase alphabets)
    static class Node 
    {
        Node[] arr = new Node[26];
        int freq;
    };
  
    // Function to insert a node in the trie
    static Node insert(String s, Node root)
    {
        int in;
        Node cur = root;
        for (int i = 0; i < s.length(); i++) 
        {
            in = s.charAt(i) - 'a';
  
            // If there is no node created then create one
            if (cur.arr[in] == null)
                cur.arr[in] = new Node();
  
            // Increase the frequency of the node
            cur.arr[in].freq++;
  
            // Move to the next node
            cur = cur.arr[in];
        }
  
        // Return the updated root
        return root;
    }
  
    // Function to return the count of Strings
    // whose prefix of length k matches with the
    // k length prefix of the given String
    static int find(String s, int k, Node root) 
    {
        int in, count = 0;
        Node cur = root;
  
        // Traverse the String
        for (int i = 0; i < s.length(); i++) 
        {
            in = s.charAt(i) - 'a';
  
            // If there is no node then return 0
            if (cur.arr[in] == null)
                return 0;
  
            // Else traverse to the required node
            cur = cur.arr[in];
  
            count++;
  
            // Return the required count
            if (count == k)
                return cur.freq;
        }
        return 0;
    }
  
    // Driver code
    public static void main(String[] args) 
    {
        String arr[] = { "abba", "abbb", "abbc", 
                        "abbd", "abaa", "abca" };
        int n = arr.length;
  
        Node root = new Node();
  
        // Insert the Strings in the trie
        for (int i = 0; i < n; i++)
            root = insert(arr[i], root);
  
        // Query 1
        System.out.print(find("abbg", 3, root) + "\n");
  
        // Query 2
        System.out.print(find("abg", 2, root) + "\n");
  
        // Query 3
        System.out.print(find("xyz", 2, root) + "\n");
  
    }
}
  
// This code is contributed by PrinciRaj1992

Python3

# Python3 implementation of the approach 
  
# Trie node (considering only lowercase alphabets) 
class Node :
    def __init__(self):
        self.arr = [None]*26
        self.freq = 0
      
class Trie:
      
    # Trie data structure class 
    def __init__(self): 
        self.root = self.getNode() 
  
    def getNode(self): 
      
        # Returns new trie node (initialized to NULLs) 
        return Node()
  
    # Function to insert a node in the trie 
    def insert(self, s): 
          
        _in = 0
        cur = self.root 
        for i in range(len(s)): 
            _in = ord(s[i]) - ord('a') 
  
            # If there is no node created then create one 
            if not cur.arr[_in]:
                cur.arr[_in] = self.getNode() 
  
            # Increase the frequency of the node 
            cur.arr[_in].freq += 1
  
            # Move to the next node 
            cur = cur.arr[_in] 
  
    # Function to return the count of strings 
    # whose prefix of length k matches with the 
    # k length prefix of the given string 
    def find(self, s, k): 
          
        _in = 0
        count = 0
        cur = self.root 
  
        # Traverse the string 
        for i in range(len(s)): 
            _in = ord(s[i]) - ord('a') 
  
            # If there is no node then return 0 
            if cur.arr[_in] == None: 
                return 0
  
            # Else traverse to the required node 
            cur = cur.arr[_in] 
  
            count += 1
  
            # Return the required count 
            if count == k: 
                return cur.freq 
        return 0
  
# Driver code 
def main(): 
      
    arr = [ "abba", "abbb", "abbc", "abbd", "abaa", "abca" ] 
    n = len(arr)
  
    root = Trie(); 
  
    # Insert the strings in the trie 
    for i in range(n): 
        root.insert(arr[i]) 
  
    # Query 1 
    print(root.find("abbg", 3)) 
  
    # Query 2 
    print(root.find("abg", 2)) 
  
    # Query 3 
    print(root.find("xyz", 2))
  
if __name__ == '__main__': 
    main() 
      
# This code is contributed by divyamohan123

C#

// C# implementation of the approach
using System;
  
class GFG 
{
  
    // Trie node (considering only lowercase alphabets)
    public class Node 
    {
        public Node[] arr = new Node[26];
        public int freq;
    };
  
    // Function to insert a node in the trie
    static Node insert(String s, Node root)
    {
        int iN;
        Node cur = root;
        for (int i = 0; i < s.Length; i++) 
        {
            iN = s[i] - 'a';
  
            // If there is no node created then create one
            if (cur.arr[iN] == null)
                cur.arr[iN] = new Node();
  
            // Increase the frequency of the node
            cur.arr[iN].freq++;
  
            // Move to the next node
            cur = cur.arr[iN];
        }
  
        // Return the updated root
        return root;
    }
  
    // Function to return the count of Strings
    // whose prefix of length k matches with the
    // k length prefix of the given String
    static int find(String s, int k, Node root) 
    {
        int iN, count = 0;
        Node cur = root;
  
        // Traverse the String
        for (int i = 0; i < s.Length; i++) 
        {
            iN = s[i] - 'a';
  
            // If there is no node then return 0
            if (cur.arr[iN] == null)
                return 0;
  
            // Else traverse to the required node
            cur = cur.arr[iN];
  
            count++;
  
            // Return the required count
            if (count == k)
                return cur.freq;
        }
        return 0;
    }
  
    // Driver code
    public static void Main(String[] args) 
    {
        String []arr = { "abba", "abbb", "abbc", 
                        "abbd", "abaa", "abca" };
        int n = arr.Length;
  
        Node root = new Node();
  
        // Insert the Strings in the trie
        for (int i = 0; i < n; i++)
            root = insert(arr[i], root);
  
        // Query 1
        Console.Write(find("abbg", 3, root) + "\n");
  
        // Query 2
        Console.Write(find("abg", 2, root) + "\n");
  
        // Query 3
        Console.Write(find("xyz", 2, root) + "\n");
  
    }
}
  
// This code is contributed by 29AjayKumar

输出：

4
6
0

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