The study is an open-label, single-center, multiple-arm investigation of a fixed-dose combination [FDC] of grazoprevir 100mg + elbasvir 50mg, and SOF 400mg, in treatment-naive participants with chronic HCV GT1 or GT3. The impact of study treatment regimens of varying duration on SVR12 (undetectable HCV ribonucleic acid [RNA] 12 weeks after ending study treatment) in cirrhotic (C) participants and non-cirrhotic (NC) participants will be determined (Part A). Any HCV GT1 participant from study Arms 1-4 in Part A who experienced virologic relapse will be offered retreatment consisting of 12 additional weeks of treatment with MK-5172/MK-8742 + SOF + ribavirin and 24 weeks of follow-up in Part B.