package net.yk.mlgorithm;
/**
* 求较大数的阶乘
* @author Administrator
*
* @param <T>
*/
public class ArraysMul<T> {
public static void main(String[] args) {
int[] array = factorial(1000);
printNum(array);
}
/**
* 计算两个两组的乘
* @param a
* @param b
* @return 用数组表示的数字
*/
public static int[] mul(int a[], int b[]) {
int alen = a.length;
int blen = b.length;
int temp = 0;
int len = alen + blen;
int t[] = new int[len];
for (int i = 0; i <= len - 1; i++) {
t[i] = 0;
}
for (int i = 0; i <= alen - 1; i++) {
for (int j = 0; j <= blen - 1; j++) {
temp = a[i] * b[j];
t[j + i] += temp;
}
}
// 将t数组大于10的进行进位操作
carryBit(t);
return t;
}
/**
* 将数组表示的数字，每位进行进位操作
* @param a
*/
static void carryBit(int a[]) {
int len = a.length;
int temp;
for (int i = 0; i <= len - 2; i++) {
temp = a[i];
if (temp >= 10) {
a[i] = temp % 10;
a[i + 1] = a[i + 1] + temp / 10;
}
}
}
/**
* 打印出数字
* @param a
*/
static void printNum(int a[]) {
int len = a.length;
int f = 0;
for (int i = len - 1; i >= 0; i--) {
if (a[i] > 0)
f = 1;
if (f > 0) {
System.out.print(a[i]);
}
}
}
/**
* * 将一个数字转换为数字表示
* @param n
* @return
*/
static int[] divideNumToArray(int n) {
int bit = bits(n);
int[] array = new int[bit];
int i = 0;
do {
array[i++] = n % 10;
n = n / 10;
} while (n > 0);
return array;
}
/**
* 返回一个数字有多少位
* @param n
* @return
*/
static int bits(int n) {
int cnt = 0;
while (n > 0) {
n = n / 10;
cnt++;
}
return cnt;
}
/**
* 求n的阶乘
* @param n
* @return
*/
static int[] factorial(int n){
int[] result = {1} ;
if(n<0) {
System.out.println("input error");
return null;
}
if(n ==0){
result = new int[0];
result[0] = 1;
return result;
}
int bit = bits(n);
int temp[] = new int[bit];
for(int i=1;i<=n;i++){
temp = divideNumToArray(i);
result = mul(temp, result);
}
return result;
}
}