C++ || Map and sets || easy solution
\n map<int,set<int>> m;  \n    unordered_map<int,int> mp;\n    NumberContainers() {\n        \n    }\n    \n    void change(int index, int number) {\n       \n 
```\n map<int,set<int>> m;  \n    unordered_map<int,int> mp;\n    NumberContainers() {\n        \n    }\n    \n    void change(int index, int number) {\n       \n        if(mp[index])\n        {\n            m[mp[index]].erase(index);\n        }\n         m[number].insert(index);\n        mp[index]=number;\n    }\n    \n    int find(int number) {\n        if(m[number].empty()) return -1;\n        return *m[number].begin();\n    }\n};\n```
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