回溯 + 剪枝 // write code here if len(s)<4 || len(s)>12{ //剪枝 return nil } res, path := []string{}, []string{} backtrack(s, 0, path, &res) return res } func backtrack(s string, startIndex int, path []string, res *[]string){ //终止条件 if startIndex == len(s...