feat: add leibniz formula

README.md

@@ -7,5 +7,6 @@
 | ModularInv              | 求乘法逆元【扩展欧几里得法】     | -                                                                                                                           |
 | Sqrt10                  | 求 $\sqrt{10}$【连分数】 | [resolve-sqrt-10](https://hatter.ink/static/resource/muboard/?id=resolve-sqrt-10&version=latest&full=1)                     |
 | WallisProduct           | 沃里斯乘积              | [wallis-product](https://hatter.ink/static/resource/muboard/?id=wallis-product&version=latest&full=1)                       |
+| LeibnizFormula          | $\pi$ 的莱布尼茨公式      | [leibniz-formula](https://hatter.ink/static/resource/muboard/?id=leibniz-formula&version=1)                                 |
 | EulerNumber             | 欧拉数                | [eulers-number](https://hatter.ink/static/resource/muboard/?id=eulers-number&version=latest&full=1)                         |
 | BirthdayParadox         | 生日悖论               | [birthday-paradox](https://hatter.ink/static/resource/muboard/?id=birthday-paradox&version=latest&full=1)                   |

src/main/java/me/hatter/math/LeibnizFormula.java

@@ -0,0 +1,27 @@
+package me.hatter.math;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+
+public class LeibnizFormula {
+
+    public static void main(String[] args) {
+        // 3.1415925535897932384628933832795028810721693993752011334749445868976601562867023677686597593566430148
+        System.out.println(pi());
+    }
+
+    public static BigDecimal pi() {
+        BigDecimal p = BigDecimal.ZERO;
+
+        for (long i = 0; i < 10000000; i++) {
+            BigDecimal v = BigDecimal.ONE.divide(BigDecimal.valueOf(i * 2 + 1), 100, RoundingMode.FLOOR);
+            if (i % 2 == 0) {
+                p = p.add(v);
+            } else {
+                p = p.subtract(v);
+            }
+        }
+
+        return p.multiply(BigDecimal.valueOf(4)).divide(BigDecimal.ONE, 100, RoundingMode.FLOOR);
+    }
+}