Reverse map lookup

Question

I have a 1 to 1 map. What\'s the best way to find keys from values,

i.e.

For examples if the map is this

KEY VALUE

a    1
b    2
c          


        

Answer 1

Given a std::map from keys to values, the following function will return a reverse lookup table, a std::map from values to keys.

    /// Given a map from keys to values, creates a new map from values to keys 
    template
    static map reverse_map(const map& m) {
        map r;
        for (const auto& kv : m)
            r[kv.second] = kv.first;
        return r;
    }