tp2 solution

Author: ctruchi

tp2/src/main/kotlin/fmt/kotlin/fundamentals/Tp2.kt

@@ -1,8 +1,75 @@
 package fmt.kotlin.fundamentals
 
+import kotlin.text.Typography.prime
+
 class Tp2 {
 
     fun getFirstPrimeNumbers(nbToFind: Int): List<Int> {
-        return arrayListOf<Int>()
+        // The list containing all the prime numbers we found
+        // It is a val because we will modify the array but not build a new array each time we add something to it
+        val primeNumbers = arrayListOf<Int>()
+
+        // Start with 2 as 0 and 1 are not prime numbers
+        // n is a var because we will change it at the end of each loop to test the next number
+        var n = 2
+
+        // Iterate while we don't have enough prime numbers in the list we want to return
+        while (primeNumbers.size < nbToFind) {
+            var prime = true
+
+            // Iterate over every number until the one we want to test to see if it can be divided
+            for (i in 2..n - 1) {
+                if (n % i == 0) {
+                    prime = false
+                    // It if can be divided once, no need to test other numbers
+                    break
+                }
+            }
+
+            // Add it to the list we want to return, if we did not find a divisor
+            if (prime) {
+                primeNumbers.add(n)
+            }
+
+            // We try the next number
+            n++
+        }
+
+        return primeNumbers
+    }
+
+    fun getFirstPrimeNumbersBetter(nbToFind: Int): List<Int> {
+        // The list containing all the prime numbers we found
+        // It is a val because we will modify the array but not build a new array each time we add something to it
+        val primeNumbers = arrayListOf<Int>()
+
+        // Start with 2 as 0 and 1 are not prime numbers
+        // n is a var because we will change it at the end of each loop to test the next number
+        var n = 2
+
+        // Iterate while we don't have enough prime numbers in the list we want to return
+        while (primeNumbers.size < nbToFind) {
+            // Add it to the list we want to return, if we did not find a divisor
+            if (isPrime(n, primeNumbers)) {
+                primeNumbers.add(n)
+            }
+
+            // We try the next number
+            n++
+        }
+
+        return primeNumbers
+    }
+
+    private fun isPrime(n: Int, primeNumbers: List<Int>): Boolean {
+        for (i in primeNumbers) {
+            if (canBeDivided(n, i)) {
+                // It if can be divided once, no need to test other numbers
+                return false
+            }
+        }
+        return true
     }
+
+    private fun canBeDivided(n: Int, i: Int) = n % i == 0
 }

tp2/src/test/kotlin/fmt/kotlin/fundamentals/Tp2Test.kt

@@ -122,6 +122,116 @@ class Tp2Test {
                 )
             )
         }
+
+        @Test
+        fun `should return 100 first prime numbers better`() {
+            val numbers = tp2.getFirstPrimeNumbersBetter(100)
+
+            expectThat(numbers).isEqualTo(
+                listOf(
+                    2,
+                    3,
+                    5,
+                    7,
+                    11,
+                    13,
+                    17,
+                    19,
+                    23,
+                    29,
+                    31,
+                    37,
+                    41,
+                    43,
+                    47,
+                    53,
+                    59,
+                    61,
+                    67,
+                    71,
+                    73,
+                    79,
+                    83,
+                    89,
+                    97,
+                    101,
+                    103,
+                    107,
+                    109,
+                    113,
+                    127,
+                    131,
+                    137,
+                    139,
+                    149,
+                    151,
+                    157,
+                    163,
+                    167,
+                    173,
+                    179,
+                    181,
+                    191,
+                    193,
+                    197,
+                    199,
+                    211,
+                    223,
+                    227,
+                    229,
+                    233,
+                    239,
+                    241,
+                    251,
+                    257,
+                    263,
+                    269,
+                    271,
+                    277,
+                    281,
+                    283,
+                    293,
+                    307,
+                    311,
+                    313,
+                    317,
+                    331,
+                    337,
+                    347,
+                    349,
+                    353,
+                    359,
+                    367,
+                    373,
+                    379,
+                    383,
+                    389,
+                    397,
+                    401,
+                    409,
+                    419,
+                    421,
+                    431,
+                    433,
+                    439,
+                    443,
+                    449,
+                    457,
+                    461,
+                    463,
+                    467,
+                    479,
+                    487,
+                    491,
+                    499,
+                    503,
+                    509,
+                    521,
+                    523,
+                    541
+                )
+            )
+        }
     }
 
 }