The molestation memoir is a much treaded upon genre, a favorite of Oprah and teen readers primed on V.C. Andrews. It’s a genre whose sharpness is wilted by all of its fictionalized versions, with despicable storylines and inevitable grotesqueries that put it always at risk of melodrama. Good literature so often relies on moral ambiguity, and the sexual violation of children is hardly a topic that inspires equivocating sympathy. But “Tiger, Tiger,’’ the debut memoir by Margaux Fragoso, is saved from schmaltz. It reads like a revised “Lolita,’’ told from the point of view of Dolores Haze rather than Humbert Humbert — a Dolores who chooses a PhD over a trailer park pregnancy. In “Tiger, Tiger,’’ Fragoso has given us the definitive portrait of both ruined innocence and misplaced empathy. The book is so powerful because it’s a work of verified truth, authored by the victim under her own name. Fragoso forces us to confront the dark world that exists just barely behind the bright one.