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@@ -0,0 +1,54 @@
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+package me.yoqi;
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+
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+import java.math.BigInteger;
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+
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+public class Test {
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+
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+ public static void main(String args[]) {
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+ int init = 25;
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+ double pk = 0;
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+ for (int n = 3; n < init; n++) {
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+ BigInteger nn = new BigInteger(String.valueOf(Math.pow(365, n)));
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+ long temp = (combination(365, n).multiply(factorial(n)).divide(nn)).longValue();
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+ pk = 1 - temp;
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+ if (pk >= 0.5) {
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+ System.out.println("最小K：" + n);
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+ break;
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+ }
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+ }
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+ System.out.print(factorial(25));
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+ }
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+
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+ /**
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+ * 计算阶乘数，即n! = n * (n-1) * ... * 2 * 1
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+ *
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+ * @param n
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+ * @return
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+ */
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+ private static BigInteger factorial(int n) {
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+ BigInteger nn=new BigInteger(Integer.toString(n));
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+ return (BigInteger) ((n > 1) ? factorial(n - 1).multiply(nn) : 1);
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+ }
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+
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+ /**
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+ * 计算排列数，即A(n, m) = n!/(n-m)!
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+ *
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+ * @param n
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+ * @param m
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+ * @return
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+ */
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+ public static BigInteger arrangement(int n, int m) {
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+ return (BigInteger) ((n >= m) ? factorial(n).divide(factorial(n - m)) : 0);
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+ }
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+
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+ /**
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+ * 计算组合数，即C(n, m) = n!/((n-m)! * m!)
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+ *
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+ * @param n
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+ * @param m
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+ * @return
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+ */
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+ public static BigInteger combination(int n, int m) {
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+ return (BigInteger) ((n >= m) ? factorial(n).divide(factorial(n - m)).divide(factorial(m)) : 0);
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+ }
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+}
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