Data commit

Task/Mertens-function/V-(Vlang)/mertens-function.v

@@ -0,0 +1,65 @@
+fn mertens(t int) ([]int, int, int) {
+    mut to:=t
+    if to < 1 {
+        to = 1
+    }
+    mut merts := []int{len:to+1}
+    mut primes := [2]
+    mut sum := 0
+    mut zeros := 0
+    mut crosses := 0
+    for i := 1; i <= to; i++ {
+        mut j := i
+        mut cp := 0      // counts prime factors
+        mut spf := false // true if there is a square prime factor
+        for p in primes {
+            if p > j {
+                break
+            }
+            if j%p == 0 {
+                j /= p
+                cp++
+            }
+            if j%p == 0 {
+                spf = true
+                break
+            }
+        }
+        if cp == 0 && i > 2 {
+            cp = 1
+            primes << i
+        }
+        if !spf {
+            if cp%2 == 0 {
+                sum++
+            } else {
+                sum--
+            }
+        }
+        merts[i] = sum
+        if sum == 0 {
+            zeros++
+            if i > 1 && merts[i-1] != 0 {
+                crosses++
+            }
+        }
+    }
+    return merts, zeros, crosses
+}
+
+fn main() {
+    merts, zeros, crosses := mertens(1000)
+    println("Mertens sequence - First 199 terms:")
+    for i := 0; i < 200; i++ {
+        if i == 0 {
+            print("    ")
+            continue
+        }
+        if i%20 == 0 {
+            println('')
+        }
+        print("  ${merts[i]:2}")
+    }
+    println("\n\nEquals zero $zeros times between 1 and 1000")
+    println("\nCrosses zero $crosses times between 1 and 1000")
+}