Created
January 25, 2021 14:53
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円周率を正確に求めるプログラム
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/* | |
* 円周率を正確に求めるプログラム | |
* | |
* - 半径が10^nの円の第一象限を縦横に10^n分割してその面積の下限と上限を求めます | |
*/ | |
#include <cstdint> | |
#include <cmath> | |
#include <iostream> | |
using INT = std::int32_t; | |
constexpr INT N = 4; | |
constexpr INT M = std::pow(10, N); | |
constexpr INT MM = M * M; | |
INT calc_lower() { | |
// 下限を求める。各分割の左上が円に含まれるならば積分する。 | |
INT sum = 0; | |
for (INT i = 1; i <= M; ++i) | |
for (INT j = 1; j <= M; ++j) | |
if (i * i + j * j <= MM) | |
sum += 1; | |
return sum * 4; | |
} | |
INT calc_upper() { | |
// 上限を求める。各分割の右下が円に含まれないならば積分する。 | |
INT sum = 0; | |
for (INT i = 0; i < M; ++i) | |
for (INT j = 0; j < M; ++j) | |
if (i * i + j * j > MM) | |
sum += 1; | |
return (MM - sum) * 4; | |
} | |
int main() { | |
std::cout << "n = " << N << std::endl; | |
std::cout << "lower = " << calc_lower() << " / " << MM << std::endl; | |
std::cout << "upper = " << calc_upper() << " / " << MM << std::endl; | |
return 0; | |
} |
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