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class Solution {
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  unordered_map<string, vector<char>> m;
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 public:
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  bool dfs(string bot, int i, string tem) {
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    if (bot.size() == 1) return true;
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    if (i == bot.size() - 1) {
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      string st;
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      return dfs(tem, 0, st);
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    }
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    for (auto v : m[bot.substr(i, 2)]) {
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      tem.push_back(v);
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      if (dfs(bot, i + 1, tem)) {
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        return true;
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      }
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      tem.pop_back();
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    }
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    return false;
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  }
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  bool pyramidTransition(string bottom, vector<string> &allowed) {
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    for (auto a : allowed) {
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      m[a.substr(0, 2)].push_back(a[2]);
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    }
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    string te;
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    return dfs(bottom, 0, te);
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  }
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};