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Question A- Codeforces Round #661 Div 3 -A. Remove Smallest Solution with Hindi Explanation - YouTube
Question B- Codeforces Round #661 Div 3 -B. Gifts Fixing - Solution with Hindi Explanation - YouTube
Question C- Codeforces Round #661 Div 3 -C. Boats Competition - Solution with Hindi Explanation - YouTube
Question D- Codeforces Round #661 Div 3 - D - Binary String To Subsequences - Solution with Hindi Explanation - YouTube
Tip for question C lies in Constraints , it can be done very easily