easy short code || using only single map || no set
mapmap;\n    NumberContainers() {\n        \n    }\n    \n    void change(int index, int number) {\n        \n        map[index]=number;\n    }\n    \n    int f
map<long long,long long>map;\n    NumberContainers() {\n        \n    }\n    \n    void change(int index, int number) {\n        \n        map[index]=number;\n    }\n    \n    int find(int number) {\n        \n        for(auto itr:map)\n        {\n            if(itr.second==number)\n            {\n                return itr.first;\n            }\n        }\n        return -1;\n    }
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