algorithm_basic_java/src/test/java/algorithm/basicMath/FindPrimeNumTest.java at master · jbee37142/algorithm_basic_java · GitHub

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packagealgorithm.basicMath;

importorg.junit.Test;

importstaticorg.hamcrest.CoreMatchers.is;
importstaticorg.junit.Assert.assertThat;

publicclassFindPrimeNumTest {

/*
 TASK
 주어지는 수 이하의 소수 개수를 구한다.
 */

@Test
publicvoidtest() {
assertThat(solution(-3), is(-1));
assertThat(solution(0), is(0));
assertThat(solution(1), is(0));
assertThat(solution(2), is(1));
assertThat(solution(3), is(2));
assertThat(solution(8), is(4));
assertThat(solution(12), is(5));
assertThat(solution(44), is(14));
//2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43
 }

publicintsolution(intnum) {
if (num < 0) {
return -1;
 }
int[] checkList = newint[num + 1];

for (inti = 2; i <= num; i++) {
checkList[i] = i;
 }
intbaseNum = (int) Math.sqrt(num);

for (inti = 2; i <= baseNum; i++) {
if (checkList[i] == 0) {
continue;
 }
for (intk = i; k <= num; k += i) {
if (checkList[k] != i && checkList[k] % i == 0) {
checkList[k] = 0;
 }
 }
 }

intcount = 0;
for (inti = 0; i <= num; i++) {
if (checkList[i] != 0) {
count++;
 }
 }

returncount;
 }
}