Fish

Fish.go

@@ -0,0 +1,25 @@
+package codility
+
+// https://codility.com/programmers/task/fish/
+func Fish(A []int, B []int) int {
+	n := len(A)
+	count := n
+	downStack := make([]int, 0)
+	for i := 0; i < n; i++ {
+		if B[i] == 1 {
+			downStack = append(downStack, A[i]) // stack push
+		} else {
+			j := len(downStack) - 1
+			// eats downstream fish, downstack pop
+			for ; j >= 0 && downStack[j] < A[i]; j-- {
+				count--
+			}
+			// if downstream fish is not eaten up, then the current upstream fish must be eaten
+			if j >= 0 {
+				count--
+			}
+			downStack = downStack[:j+1]
+		}
+	}
+	return count
+}

example_test.go

@@ -6,6 +6,23 @@ import (
 	"testing"
 )
 
+func ExampleFish() {
+	A, B := make([]int, 5), make([]int, 5)
+	A[0] = 4
+	A[1] = 3
+	A[2] = 2
+	A[3] = 1
+	A[4] = 5
+
+	B[0] = 0
+	B[1] = 1
+	B[2] = 0
+	B[3] = 0
+	B[4] = 0
+	fmt.Println(Fish(A, B))
+	// Output: 2
+}
+
 func ExampleNumberOfDiscIntersections() {
 	A := make([]int, 6)
 	A[0] = 1