Count of strings whose prefix match with the given string to a given length k

// C++ implementation of the approach
#include <bits/stdc++.h>
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;
}

#include <bits/stdc++.h>
using namespace std;

class Solution {
public:
    int klengthpref(string arr[], int n, int k, string str)
    {

        string a = str.substr(
            0, k); // storing k-length substring of str
        int count
            = 0; // counter to count the matching condition

        // looping through each word of arr
        for (int i = 0; i < n; i++) {
            if (arr[i].length()
                < k) // if the length of string from arr is
                     // less than k
                continue; // then there is no point in
                          // finding the substring so we
                          // skip
            string b = arr[i].substr(
                0, k); // storing k-length substring of each
                       // string from arr
            if (a == b) // checking equality of the two
                        // substring a and b
                count++; // if condition matches increase
                         // the counter
        }

        return count; // finally return the count
    }
};

int main()
{
    string arr[] = { "abba", "abbb", "abbc",
                     "abbd", "abaa", "abca" };
    string str = "abbg";
    int n = sizeof(arr) / sizeof(string), k = 3;

    Solution ob;
    cout << ob.klengthpref(arr, n, k, str);

    return 0;
}

#include <iostream>
#include <string>
#include <vector>
using namespace std;

// Function to count the number of strings in the vector 'arr' that have a matching prefix of length 'k' with the input string 'str'
int PrefixMatchCount(vector<string>& arr, string str, int k) {
    int count = 0; // Initialize a variable to store the count of matching strings
    for (const string& s : arr) { // Iterate through each string 's' in the vector 'arr' using a range-based for loop
        if (s.substr(0, k) == str.substr(0, k)) { // Check if the first 'k' characters of 's' and 'str' are equal
            count++; // If there is a match, increment the count variable
        }
    }
    return count; // Return the final count of matching strings
}

int main() {
    vector<string> arr = { "abba", "abbb", "abbc", "abbd", "abaa", "abca" }; // Initialize a vector 'arr' containing some strings
    string str = "abbg"; // Initialize the input string 'str'
    int k = 3; // Initialize the prefix length 'k'
    cout << PrefixMatchCount(arr, str, k) << endl; // Call the PrefixMatchCount function and print the result
    return 0; // Exit the program with status 0
}