1. 1768. Merge Strings Alternately.java

 public String mergeAlternately(String word1, String word2) {
        StringBuilder sb = new StringBuilder();
        int m = word1.length();
        int i =0;
        int n = word2.length();

        while(i<m || i<n){
            if(i<m){
                sb.append(word1.charAt(i));
            }
           if(i<n){
             sb.append(word2.charAt(i));
           }
           i++;
        }
       return sb.toString(); 
    }