A-M baby

Task/Filter/Go/filter.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+    "fmt"
+    "math/rand"
+)
+
+func main() {
+    a := rand.Perm(20)
+    fmt.Println(a)       // show array to filter
+    fmt.Println(even(a)) // show result of non-destructive filter
+    fmt.Println(a)       // show that original array is unchanged
+    reduceToEven(&a)     // destructive filter
+    fmt.Println(a)       // show that a is now changed
+    // a is not only changed, it is changed in place.  length and capacity
+    // show that it still has its original allocated capacity but has now
+    // been reduced in length.
+    fmt.Println("a len:", len(a), "cap:", cap(a))
+}
+
+func even(a []int) (r []int) {
+    for _, e := range a {
+        if e%2 == 0 {
+            r = append(r, e)
+        }
+    }
+    return
+}
+
+func reduceToEven(pa *[]int) {
+    a := *pa
+    var last int
+    for _, e := range a {
+        if e%2 == 0 {
+            a[last] = e
+            last++
+        }
+    }
+    *pa = a[:last]
+}