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();
  }
}