1768. Merge Strings Alternately

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Two Pointers String

Time: O(m+n)

Space: O(m+n)

Intuition

Merge two strings alternately: take one character from each string in turns.

Algorithm

1Two pointers i=0, j=0. Alternate appending word1[i] and word2[j]. Append remaining characters.

Common Pitfalls

•When one string runs out, append remaining characters of the other.

1768.cs

// Approach: Two-pointer alternating append, then append remainder of whichever string is longer.
// Time: O(m+n) Space: O(m+n)

public class Solution
{
    public string MergeAlternately(string word1, string word2)
    {
        int l1 = 0, l2 = 0;
        int r1 = word1.Length;
        int r2 = word2.Length;

        StringBuilder res = new StringBuilder();
        while (l1 < r1 && l2 < r2)
        {
            res.Append(word1[l1++]);
            res.Append(word2[l2++]);
        }

        while (l1 < r1)
            res.Append(word1[l1++]);

        while (l2 < r2)
            res.Append(word2[l2++]);

        return res.ToString();
    }
}

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