LeetCode/java/merge-strings-alternately.java

class Solution {
    public String mergeAlternately(String word1, String word2) {
        StringBuilder sb = new StringBuilder(word1.length() + word2.length());

        int i, j;
        for (i = 0, j = 0; i < word1.length() && j < word2.length(); ++i, ++j) {
            sb.append(word1.charAt(i));
            sb.append(word2.charAt(j));
        }

        if (i < word1.length()) {
            sb.append(word1.substring(i));
        }
        if (j < word2.length()) {
            sb.append(word2.substring(j));
        }

        return sb.toString();
    }
}