This sentence is forced (most probably to teach you the dislike's translation), but it is totally odd for a native Ro speaker. We would never say it, preferring the more straight "she didn't like me", "ea nu m-a plăcut" (or depending on context, like marriage, things happened long ago, etc, "ea nu m-a vrut", "ea nu m-a iubit" etc.)
But most probably, you will hear the semantic-equivalent "Lui/Ei nu i-a plăcut de mine”. (”He/She didn't like me”, the 'dative' construction like in German, etc)
Related to your question, yes, grammatically, "(eu) i-am displăcut (ei/lui)" is quite correct, and it has a higher chance to be heard in a Romanian discussion than Duo's phrase has (higher, like in 1% instead of 0.00001%).
Thanks for the detailed answer. I am surprised by your example using "plăcut" though: to me, "a place" is constructed backwards: the subject is what is being liked, not the object. The construction would be the same as "plaire" in French, "gustar" in Spanish or "gefallen" in German. What you are saying is that you can use "a place" with the subject being the person that likes the object. Do I understand you well?
yes, we can say it both ways, and both are right. Romanian language is a very rich language, with over a million words (as opposed to English, with only about 200 thousands (see official word lists for Scrabble championships, like SOWPODS, TWL, LOC). We were (geographically, politically and lingustically) at the confluence of few big empires along the centuries, and the language, Latin based, got enriched with elements of Greek, Slavic, Turkish, oriental, etc. from east, and French, German, Hungarian, occidental, from west, all on top of the old Dacian language from which we still keep like 6-10% or so. This means inclussive grammar, not only vocabulary. For example, in Romanian we have some "strange" verbs which are either pure transitive (like "to wash") and some other which are pure reflective (like "to laugh"), and some other which are both (like "to like"). Such verbs can only be used in active diathesis (https://en.wikipedia.org/wiki/Voice_(grammar)), or only in passive, or only in reflexive diathesis (yes, we have that too, in spite of the fact that the linguists are still arguing about it, see https://ro.wikipedia.org/wiki/Diatez%C4%83_(gramatic%C4%83)). In this case "a place" (to like) can be used in both the "dative" and "nominative" constructions, and you will hear both, depending on context, speaker, etc. For example:
Ea mă place - She likes me. (Ei ii place de mine, nominative/tranzitive/active construction)
Ea îmi place - I like her. (Mie imi place de ea, She is dear/pleasant to me) - dative/pasive construction
(no, there is no mistake, all forms are correct, and common)
Edit: just now I see, re-reading your first message, where the confussion is comming from: your sentence ”ea m-a plăcut” is correct in Romanian and it means ”She liked me”, and not the other way around. NOT ”I liked her”. I was the object of the action. Any time you see ”mă” ori the past ”m-a” (contraction of ”mă” and ”to have”, this is how we form the past), you have to think to accusative, ”pe mine mă” (or ”m-a”, the object of the action). This ”pe mine” is always there, with ”mă”, even if we write it or not. For example, ”I go gome”, is ”Eu mă duc acasă”, it has the meaning ”eu mă duc [pe mine] acasă”, I carry myself home, as opposite of carrying you home (which would be ”eu te duc [pe tine] acasă”.
”Ea mă place [pe mine]" or "[Pe mine] mă place ea” ori ”Ea [pe mine] mă place” means the same thing and all are correct, with or without the bracket's content, and using one or another depends of what you want to stress - She likes me. Same meaning as "Ei de mine îi place”, but this time with dative, etc. When you see the dative ”mie”, think to the german ”[gefällt] mir”. In English, ”to me”. Therefore, ”Mie imi place de ea” would mean ”I like her”. ”She is dear to me”.
When you bring the past, be careful:
Ea m-a plăcut = She liked me (ea m-a plăcut pe mine, ea pe mine m-a plăcut)
Ea mi-a plăcut = I liked her (ea mi-a plăcut mie, ea mie mi-a plăcut)
In the first sentence the ”m-” is a contraction of accusative ”[pe mine] mă”, but the ”mi-” is a contraction from dative ”[mie] îmi”
i gather from all your very interesting and detailed answer that WE CAN DROP PE MINE MOST OF`THE TIME IF NOT ALWAYS ? This would make things easier fro us, even though, a s native french speaker and having spanish as my second mother tongue, i can easily understand the way Romanian formulates these sentences, though they are not natural to me. So, please, can I drop PE MINE ?