누적합(Prefix Sum) 쉬운 설명
참고
https://eine.tistory.com/entry/2%EC%B0%A8%EC%9B%90-%EB%88%84%EC%A0%81%ED%95%A9-%EB%B6%80%EB%B6%84%ED%95%A9-%EA%B5%AC%ED%95%98%EA%B8%B0
https://nahwasa.com/entry/%EB%88%84%EC%A0%81-%ED%95%A9prefix-sum-2%EC%B0%A8%EC%9B%90-%EB%88%84%EC%A0%81%ED%95%A9prefix-sum-of-matrix-with-java