简单题--双指针

class Solution {
    public String mergeAlternately(String word1, String word2) {
        int len1=word1.length();
        int len2=word2.length();
        int vi=0;
        String ans="";


        while(vi<len1||vi<len2){
            if(vi<len1){
                ans=ans+word1.charAt(vi);
            }
            if(vi<len2){
                ans=ans+word2.charAt(vi);
            }
            vi++;
        }
        return ans;
    }
}