Iterating through one map and one multimap and printing the vlaue of common keys
You can merge both maps to a "list". That should give you O(n) complexity solution where n is a total number of elements in both maps.
map elements are sorted from lower to higher, so simple iteration would yield an ordered list.
To merge maps, you need to iterate both of the maps, instead of insertion to a list, you can just output values to the screen.