solves three diivisors

Author: anishLearnsToCode

README.md

@@ -468,7 +468,7 @@
 | 1935 | [Maximum Number of Words You Can Type](https://leetcode.com/problems/maximum-number-of-words-you-can-type)                                                |                                                         [![Java](assets/java.png)](src/MaximumNumberOfWordsYouCanType.java)                                                          |                                                                                                                                   |
 | 1941 | [Check if All Characters Have Equal Number of Occurrences](https://leetcode.com/problems/check-if-all-characters-have-equal-number-of-occurrences)        |                                                [![Java](assets/java.png)](src/CheckIfAllCharactersHaveEqualNumberOfOccurrences.java)                                                 |                                                                                                                                   |
 | 1945 | [Sum of Digits of String After Convert](https://leetcode.com/problems/sum-of-digits-of-string-after-convert)                                              |                                                         [![Java](assets/java.png)](src/SumOfDigitsOfStringAfterConvert.java)                                                         |                                                                                                                                   |
-| 1952 | [Three Divisors](https://leetcode.com/problems/three-divisors)                                                                                            |                                                                                                                                                                                      |                                                                                                                                   |
+| 1952 | [Three Divisors](https://leetcode.com/problems/three-divisors)                                                                                            |                                                                  [![Java](assets/java.png)](src/ThreeDivisors.java)                                                                  |                                                                                                                                   |
 | 1957 | [Delete Characters to Make Fancy String](https://leetcode.com/problems/delete-characters-to-make-fancy-string)                                            |                                                                                                                                                                                      |                                                                                                                                   |
 | 1961 | [Check If String Is a Prefix of Array](https://leetcode.com/problems/check-if-string-is-a-prefix-of-array)                                                |                                                                                                                                                                                      |                                                                                                                                   |
 | 1967 | [Number of Strings That Appear as Substrings in Word](https://leetcode.com/problems/number-of-strings-that-appear-as-substrings-in-word)                  |                                                                                                                                                                                      |                                                                                                                                   |

src/ThreeDivisors.java

@@ -0,0 +1,49 @@
+// https://leetcode.com/problems/three-divisors
+// T: O(1)
+// S: O(1)
+
+public class ThreeDivisors {
+    private static final PrimeSieve PRIME_SIEVE = PrimeSieve.ofSize(101);
+
+    public boolean isThree(int n) {
+        return isPerfectSquare(n);
+    }
+
+    private boolean isPerfectSquare(int x) {
+        int sqrt = (int) Math.sqrt(x);
+        return sqrt * sqrt == x && PRIME_SIEVE.isPrime(sqrt);
+    }
+
+    private static class PrimeSieve {
+        final byte[] sieve;
+
+        private static PrimeSieve ofSize(int size) {
+            return new PrimeSieve(size);
+        }
+
+        PrimeSieve(int size) {
+            this.sieve = new byte[size + 1];
+            initializeSieve();
+        }
+
+        public boolean isPrime(int number) {
+            return sieve[number] == 0;
+        }
+
+        private void initializeSieve() {
+            sieve[0] = 1;
+            sieve[1] = 1;
+            for (int i = 2 ; i < sieve.length ; i++) {
+                if (sieve[i] == 0) {
+                    markFactors(i);
+                }
+            }
+        }
+
+        private void markFactors(int prime) {
+            for (int i = prime * prime ; i < sieve.length ; i += prime) {
+                sieve[i] = 1;
+            }
+        }
+    }
+}