LeetCode Challenge #1768. Merge Strings Alternately

Question 1 of 75 - LeetCode Weekly Challenge

LeetCode Challenge #1768. Merge Strings Alternately

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:

1 <= word1.length, word2.length <= 100
word1 and word2 consist of lowercase English letters.

Video Solution

C++ Solution

				
					class Solution {
public:
    string mergeAlternately(string word1, string word2) {


        string finalstr="";


        int i=0,j=0;


        while(i<word1.length() and j<word2.length())
        {
            finalstr.push_back(word1[i]);
            i++;
            finalstr.push_back(word2[j]);
            j++;
        }
        while(i<word1.length())
        {
            finalstr.push_back(word1[i]);
            i++;
        }
        while(j<word2.length())
        {
            finalstr.push_back(word2[j]);
            j++;
        }


        return finalstr;


    }

Code Explanation

Our purpose is to merge the two input strings. As explained in the video, we have a string a b c d and another w x y z and the resultant will be a w b x c y d z .

Let’s see the approach step by step -:

Declared empty string finalstr (to store the merged result).
Declared int i=0, j=0 ; initial values of i and j . (i is the iterator for word1, j is the iterator for word2)
Now we’ll use while loop –

The first while loop will work if (and as long as) the value of ‘i’ is less than the length of word1 and the value of ‘j’ is less than the length of word2.
In this loop, we will pick the ‘ith’ character from word1 and push it into our resultant string(finalstr) and move ‘i’ to the next character (we used i++ for that).
Similarly, we will pick the ‘jth’ character from word2 and push it into our resultant string(finalstr) and move ‘j’ to the next character (we used j++ for that).
This will keep on working this way till we have characters left in both the strings.

As we know, if we are using multiple conditions separated by an and or && the loop will only work when all the conditions are true. This means that when the first while loop ends there might be 2 reasons for that.

-Either both strings have no characters left un-iterated

-Or either one of them has no characters left un-iterated

If both had characters left, then the loop wouldn’t have stopped (See the condition in while).

So, we will use 2 more while loops, one will iterate on the remaining characters of word1 and the other on the remaining characters of word2. This way, only one of the while loops will be executed, if word1 has characters left then 1st while loop will run, else the second one. If none of them have characters, none of the while loop will run.

So the second while loop will consider only word1 and all the remaining characters in word1 are pushed in the finalstr as it is.
Similarly, the third while loop will consider only word2 and all the remaining characters in word2 are pushed in the finalstr as it is.

And finally we will return the resultant string (finalstr).

Question 1 of 75 - LeetCode Weekly Challenge