finding prime numbers from 1 to n using eratosthenes sieve

numerical/prime_finder.go

@@ -0,0 +1,25 @@
+package main
+
+// PrimesUpTo finds all prime numbers from 1 to upperBound
+// It's implemented using eratosthenes sieve
+// Works in O(upperBound) time and space
+func PrimesUpTo(upperBound int) []int {
+	// lp array stores minimal prime divisor for every number from 2 to upperBound
+	var lp []int
+	lp = make([]int, upperBound+1)
+
+	// primes array stores primes
+	var primes []int
+
+	for i := 2; i <= upperBound; i++ {
+		if lp[i] == 0 {
+			lp[i] = i
+			primes = append(primes, i)
+		}
+		for j := 0; j < len(primes) && primes[j] <= lp[i] && i*primes[j] <= upperBound; j++ {
+			lp[i*primes[j]] = primes[j]
+		}
+	}
+
+	return primes
+}