DSA_Examples_Scratch

Leetcode Problem:

You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the other, append the additional letters onto the end of the merged string.

Return the merged string.

Example 1:

Input: word1 = "abc", word2 = "pqr"
Output: "apbqcr"
Explanation: The merged string will be merged as so:
word1:  a   b   c
word2:    p   q   r
merged: a p b q c r

Example 2:

Input: word1 = "ab", word2 = "pqrs"
Output: "apbqrs"
Explanation: Notice that as word2 is longer, "rs" is appended to the end.
word1:  a   b 
word2:    p   q   r   s
merged: a p b q   r   s

Example 3:

Input: word1 = "abcd", word2 = "pq"
Output: "apbqcd"
Explanation: Notice that as word1 is longer, "cd" is appended to the end.
word1:  a   b   c   d
word2:    p   q 
merged: a p b q c   d

Constraints:

word1 and word2 consist of lowercase English letters.

1 <= word1.length, word2.length <= 100

Solution

Memory (O(M+N)); Speed (O(M+N))

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char * mergeAlternately(char * word1, char * word2) {
    int len1 = strlen(word1);
    int len2 = strlen(word2);
    int total = len1 + len2;

    // +1 for null terminator
    char *result = (char *)malloc((total + 1) * sizeof(char));

    int i = 0, j = 0, k = 0;

    // Pick alternate characters while both strings have remaining chars
    while (i < len1 && j < len2) {
        result[k++] = word1[i++];
        result[k++] = word2[j++];
    }

    // Append remaining characters (if any)
    while (i < len1) {
        result[k++] = word1[i++];
    }
    while (j < len2) {
        result[k++] = word2[j++];
    }

    // Null terminate the merged string
    result[k] = '\0';
    return result;
}

// Example usage
int main() {
    char word1[] = "123";
    char word2[] = "pqrstu";

    char *merged = mergeAlternately(word1, word2);
    printf("Merged String: %s\n", merged);

    free(merged); // Free allocated memory
    return 0;
}