FactorialZeroCount.java

package exercise;

import org.junit.Test;

import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;

public class FactorialZeroCount {

 /*
 TASK
 n!의 결과값에서 0의 개수를 구한다.
 */

 @Test
 public void test() {

 assertThat(countZero1(getFactorial(5)), is(1));
 assertThat(countZero1(getFactorial(12)), is(2));
 assertThat(countZero2(5), is(1));
 assertThat(countZero2(12), is(2));
 }

 public int getFactorial(int num) {
 int result = 1;
 for (int i = 1; i <= num; i++) {
 result *= i;
 }
 return result;
 }

 public int countZero1(int num) {
 int count = 0;
 while (num % 10 == 0) {
 num /= 10;
 count++;
 }
 return count;
 }


 // 5가 얼마나 곱해졌는지가 중요하다.
 public int countZero2(int num) {
 int count = 0;
 for (int i = 5; i <= num; i += 5) {
 int base = i;
 while (base % 5 == 0) {
 base /= 5;
 count++;
 }
 }
 return count;
 }
}