[20251020] BOJ / G5 / Ezreal 여눈부터 가네 ㅈㅈ / 설진영#1179
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ShinHeeEul merged 1 commit intomainfrom Oct 20, 2025
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마지막 자리가 5인 3의 배수이면 무조건 15의 배수 아닌가요?? |
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🧷 문제 링크
https://www.acmicpc.net/problem/20500
🧭 풀이 시간
40분
👀 체감 난이도
✏️ 문제 설명
1과 5로만 이루어진 N자리 양의 정수 중 15의 배수 개수를 구하는 문제
🔍 풀이 방법
15의 배수 조건: 3의 배수이면서 5의 배수
1과 5로만 이루어진 수가 5의 배수가 되려면 마지막 자리가 5여야함
⏳ 회고
5의 배수 조건 때문에 마지막 자리는 무조건 5
처음엔 자릿수 합만 보면 되겠다 싶었는데 그럼 실제 수를 15로 나눴을 때 판별이 안되니까 결국 15로 나눈 나머지를 직접 추적해야됨