c++ - Swapping each pair of values in a multimap<int, int> -

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i have multimap containing on 5 million pairs , need swap keys values. 

unordered_multimap<int, int> edge;

due large size of container , processes involved, prefer not have create new multimap swapped pairs iterating on each element of map.

what best way, if any, in place?

the proper approach not @ all, instead have bi-directional map in first place, on can perform lookup in either direction.

consider looking boost.bimap.


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