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class Solution
{
public:
    string mergeAlternately(string word1, string word2)
    {
      std::string res;
      int n = word1.size(), m = word2.size();
      int i = 0, j = 0;
      while (i < n || j < m)
      {
        if (i < n) res += word1[i ++ ];
        if (j < m) res += word2[j ++ ];
      }
      return res;
    }
};