refactoring and fixing bug.

util.go

@@ -0,0 +1,53 @@
+package main
+
+import "sync"
+
+// returns all the element x that are in c1 and c2.  can retuns many time
+// the same x.
+func intersection(c1, c2 <-chan uint64) <-chan uint64 {
+	var wg sync.WaitGroup
+	out := make(chan uint64)
+
+	mc1, mc2 := make(map[uint64]bool), make(map[uint64]bool)
+
+	filter := func(c <-chan uint64, mapToAdd, mapToVerify map[uint64]bool) {
+		for n := range c {
+			mapToAdd[n] = true
+			if _, ok := mapToVerify[n]; ok {
+				out <- n
+			}
+		}
+		wg.Done()
+	}
+	wg.Add(2)
+	go filter(c1, mc1, mc2)
+	go filter(c2, mc2, mc1)
+
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+	return out
+}
+
+// remove all duplicates in inputC
+func uniq(inputC <-chan uint64) <-chan uint64 {
+	m := make(map[uint64]bool)
+	c := make(chan uint64)
+	go func() {
+		for n := range inputC {
+			if _, ok := m[n]; !ok {
+				m[n] = true
+				c <- n
+			}
+		}
+		close(c)
+	}()
+	return c
+}
+
+// returns the intersection of a and b without repetitions
+func Intersection(a, b <-chan uint64) <-chan uint64 {
+	return uniq(intersection(a, b))
+
+}