Meta Strings (Check if two strings can become same after a swap in one string)

Given two strings, the task is to check whether these strings are meta strings or not. Meta strings are the strings which can be made equal by exactly one swap in any of the strings. Equal string are not considered here as Meta strings.


Input : str1 = "geeks" 
        str2 = "keegs"
Output : Yes
By just swapping 'k' and 'g' in any of string, 
both will become same.

Input : str1 = "rsting"
        str2 = "string
Output : No

Input :  str1 = "Converse"
         str2 = "Conserve"

Asked in : Google

Below are steps used in the algorithm.

  1. Check if both strings are of equal length or not, if not return false.
  2. Otherwise, start comparing both strings and count number of unmatched characters and also store the index of unmatched characters.
  3. If unmatched characters are more than 2 then return false.
  4. Otherwise check if on swapping any of these two characters in any string would make the string equal or not.
  5. If yes then return true. Otherwise return false.
// C++ program to check if two strings are meta strings
using namespace std;

// Returns true if str1 and str2 are meta strings
bool areMetaStrings(string str1, string str2)
    int len1 = str1.length();
    int len2 = str2.length();

    // Return false if both are not of equal length
    if (len1 != len2)
        return false;

    // To store indexes of previously mismatched
    // characters
    int prev = -1, curr = -1;

    int count = 0;
    for (int i=0; i<len1; i++)
        // If current character doesn't match
        if (str1[i] != str2[i])
            // Count number of unmatched character

            // If unmatched are greater than 2,
            // then return false
            if (count > 2)
                return false;

            // Store both unmatched characters of
            // both strings
            prev = curr;
            curr = i;

    // Check if previous unmatched of string1
    // is equal to curr unmatched of string2
    // and also check for curr unmatched character,
    // if both are same, then return true
    return (count == 2 &&
            str1[prev] == str2[curr] &&
            str1[curr] == str2[prev]);

// Driver code
int main()
    string str1 = "converse";
    string str2 = "conserve";

    areMetaStrings(str1,str2) ? cout << "Yes"
                            : cout << "No";
    return 0;



Reference :

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