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C++ Program for Check if given string can be formed by two other strings or their permutations

  • Last Updated : 24 Jan, 2022

Given a string str and an array of strings arr[], the task is to check if the given string can be formed by any of the string pair from the array or their permutations.

Examples:

Input: str = “amazon”, arr[] = {“loa”, “azo”, “ft”, “amn”, “lka”}
Output: Yes
The chosen strings are “amn” and “azo”
which can be rearranged as “amazon”.

Input: str = “geeksforgeeks”, arr[] = {“geeks”, “geek”, “for”}
Output: No

Below is the implementation of the above approach:

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function that returns true if str can be
// generated from any permutation of the
// two strings selected from the given vector
bool isPossible(vector<string> v, string str)
{
  
    // Sort the given string
    sort(str.begin(), str.end());
  
    // Select two strings at a time from given vector
    for (int i = 0; i < v.size() - 1; i++) {
        for (int j = i + 1; j < v.size(); j++) {
  
            // Get the concatenated string
            string temp = v[i] + v[j];
  
            // Sort the resultant string
            sort(temp.begin(), temp.end());
  
            // If the resultant string is equal
            // to the given string str
            if (temp.compare(str) == 0) {
                return true;
            }
        }
    }
  
    // No valid pair found
    return false;
}
  
// Driver code
int main()
{
    string str = "amazon";
    vector<string> v{ "fds", "oxq", "zoa", "epw", "amn" };
  
    if (isPossible(v, str))
        cout << "Yes";
    else
        cout << "No";
  
    return 0;
}

Method 2: Counting sort can be used to reduce the running time of the above approach. Counting sort uses a table to store the count of each character. We have 26 alphabets hence we make an array of size 26 to store counts of each character in the string. Then take the characters in increasing order to get the sorted string.
Below is the implementation of the above approach:

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
#define MAX 26
  
// Function to sort the given string
// using counting sort
void countingsort(string& s)
{
    // Array to store the count of each character
    int count[MAX] = { 0 };
    for (int i = 0; i < s.length(); i++) {
        count[s[i] - 'a']++;
    }
    int index = 0;
  
    // Insert characters in the string
    // in increasing order
    for (int i = 0; i < MAX; i++) {
        int j = 0;
        while (j < count[i]) {
            s[index++] = i + 'a';
            j++;
        }
    }
}
  
// Function that returns true if str can be
// generated from any permutation of the
// two strings selected from the given vector
bool isPossible(vector<string> v, string str)
{
  
    // Sort the given string
    countingsort(str);
  
    // Select two strings at a time from given vector
    for (int i = 0; i < v.size() - 1; i++) {
        for (int j = i + 1; j < v.size(); j++) {
  
            // Get the concatenated string
            string temp = v[i] + v[j];
  
            // Sort the resultant string
            countingsort(temp);
  
            // If the resultant string is equal
            // to the given string str
            if (temp.compare(str) == 0) {
                return true;
            }
        }
    }
  
    // No valid pair found
    return false;
}
  
// Driver code
int main()
{
    string str = "amazon";
    vector<string> v{ "fds", "oxq", "zoa", "epw", "amn" };
  
    if (isPossible(v, str))
        cout << "Yes";
    else
        cout << "No";
  
    return 0;
}


Please refer complete article on Check if given string can be formed by two other strings or their permutations for more details!

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