Mariah Carey -- I Could Judge 'American Idol' ... BY MYSELF!!!!

Mariah Carey doesn't need no stinkin' co-judges on "American Idol" ... the diva tells TMZ she can do it all by her damn self!!!! And with multiple personalities, she's just the person to pull it off.

Carey spoke to photogs on both ends of the country yesterday -- first in NYC, where the paps asked about the tension between herself and Nicki Minaj.

Carey shot back, "What tension? There's no tension!" Suuuuure.

When she arrived to L.A. we asked Carey who she would like to join her on the judge's panel, since there are still 3 open chairs.

Mariah replied, "I'd answer that, but I'm not quite sure how."

When we suggested she judge the show by herself, Carey made it clear she LOVED that idea ... saying, "Naturally ... why not?"