Here are some possible influences:
J.D. Salinger: Hinton's debut novel, "The Outsiders", shares many themes with Salinger's "The Catcher in the Rye", such as alienation, teenage angst, and the search for belonging. The first-person narration and focus on the inner world of a teenager are also similarities.
Realism and Social Commentary: Hinton's focus on depicting the gritty realities of teenage life in the 1960s suggests an influence from realist writers like John Steinbeck and Harper Lee, who tackled social issues and explored the lives of ordinary people.
The Beat Generation: Hinton's use of slang and her characters' rebellion against societal norms may be influenced by the Beat Generation writers, who rejected traditional values and explored themes of nonconformity and alienation.
Young Adult Literature: Hinton's focus on teenage characters and issues paved the way for modern young adult literature and may have been influenced by earlier YA authors like Louisa May Alcott and Judy Blume.
Personal Experience: Hinton's own experiences growing up in Oklahoma and her observations of social dynamics among teenagers undoubtedly played a significant role in shaping her writing.
While we can't definitively say who influenced S.E. Hinton, it's clear that her writing draws from a range of sources, including literary traditions, social movements, and her own personal experiences.