Check whether a given string is an interleaving of two other given strings | GeeksforGeeks

Check whether a given string is an interleaving of two other given strings | GeeksforGeeks
Given three strings A, B and C. Write a function that checks whether C is an interleaving of A and B.
C is said to be interleaving A and B, if it contains all characters of A and B and order of all characters in individual strings is preserved.

Solution:
Pick each character of C one by one and match it with the first character in A. If it doesn’t match then match it with first character of B. If it doesn’t even match first character of B, then return false. If the character matches with first character of A, then repeat the above process from second character of C, second character of A and first character of B. If first character of C matches with the first character of B (and doesn’t match the first character of A), then repeat the above process from the second character of C, first character of A and second character of B. If all characters of C match either with a character of A or a character of B and length of C is sum of lengths of A and B, then C is an interleaving A and B.

Time Complexity: O(m+n) where m and n are the lengths of strings A and B respectively.

Note that the above approach doesn’t work if A and B have some characters in common.

Time Complexity: O(MN)
Auxiliary Space: O(MN)

bool isInterleaved (char *A, char *B, char *C)

{

    // Iterate through all characters of C.

    while (*C != 0)

    {

        // Match first character of C with first character of A,

        // If matches them move A to next

        if (*A == *C)

            A++;

        // Else Match first character of C with first character of B,

        // If matches them move B to next

        else if (*B == *C)

            B++;

        // If doesn't match with either A or B, then return false

        else

            return false;

         

        // Move C to next for next iteration

        C++;

    }

    // If A or B still have some characters, then length of C is smaller

    // than sum of lengths of A and B, so return false

    if (*A || *B)

        return false;

    return true;

}

Note that the above approach doesn’t work if A and B have some characters in common. For example, if string A = “AAB”, string B = “AAC” and string C = “AACAAB”, then the above method will return false. We have discussed here an extended solution that handles common characters.
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