12以内20以内100以内的阶乘方法

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<br style="font-size: 24px; font-weight: bold;" /><span style="font-size: 24px; "><strong>12以内、20以内、100以内、1000以内的阶乘方法</strong></span>

package com.firstACMTest;import java.math.BigDecimal;import java.math.BigInteger;public class 阶乘总结 {/* *  * 动态规划中的阶乘 */public static int J[] = new int[1000];public static int jiechengDT(int n) {int t = 0;if (J[n] != 0)return J[n];if (n <= 1)t = 1;if (n > 1)t = n * jiechengDT(n - 1);return J[n] = t;}/* * 20以内的阶乘普通方法 */public static Long jiecheng(int n) {if (n < 1)return 1L;return n * jiecheng(n - 1);}/* * 12以内的阶乘普通方法 */public static int jiecheng1(int n) {if (n < 1)return 1;return n * jiecheng1(n - 1);}/* * 大于20的阶乘用BigDecimal方法参数是BigDecimal类型 */public static BigDecimal factorial(BigDecimal n) {BigDecimal bd1 = new BigDecimal(1);// BigDecimal类型的1BigDecimal bd2 = new BigDecimal(2);// BigDecimal类型的2BigDecimal result = bd1;// 结果集，初值取1while (n.compareTo(bd1) > 0) {// 参数大于1，进入循环result = result.multiply(n.multiply(n.subtract(bd1)));n = n.subtract(bd2);// n-2后继续}return result;}/* * 大于20的阶乘用BigInteger方法参数是int类型 */public static BigInteger bigIntegerFactorial(int num) {BigInteger result = BigInteger.valueOf(1);// 定义大整数，初始值为1for (int i = 1; i <= num; i++) {BigInteger n = BigInteger.valueOf(i);result = result.multiply(n);}return result;}/* * 大于20的阶乘用BigInteger方法参数是String类型 此String类型必须可以转换成整数类型，或者是题目可以给出1-N的阶乘 * String值转化成BigInteger为new BigInteger(String.valueOf(i)) */public static BigInteger bigIntegerFactorial(String num) {BigInteger result = new BigInteger("1");int N = Integer.parseInt(num);for (int i = 1; i <= N; i++) {result = result.multiply(new BigInteger(String.valueOf(i)));}return result;}/* * 大于20的阶乘用BigInteger方法参数是BigInteger类型 BigInteger.ONE表示大整数 */public static BigInteger bigIntegerFactorial(BigInteger num) {BigInteger result;if (num.equals(BigInteger.ONE))return BigInteger.ONE;return num.multiply(bigIntegerFactorial(num.subtract(BigInteger.ONE)));}public static void main(String[] args) {}}

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