"Maximum Fruits Harvested After at Most K Steps" accepted solution improved by parallel execution

2106-max-fruits-harvested-in-k-steps.go

@@ -1,5 +1,96 @@
 package main
 
+import "sync"
+
+func fromRightToLeft(fruityPrefix []int, startPos int, k int, leftLimit int, rightLimit int, pwg *sync.WaitGroup, presult *int) {
+	calcFruitySliceSum := func(begin int, end int) int {
+		begin--
+		if begin < 0 {
+			return fruityPrefix[end]
+		}
+
+		return fruityPrefix[end] - fruityPrefix[begin]
+	}
+
+	windowSize := k / 2
+	maxFruits := calcFruitySliceSum(startPos, rightLimit)
+
+	delta := k - windowSize*2
+	windowBegin :=
+		startPos - delta // in case number of steps cannot be fully divided by 2, start position is shifted 1 position to the left
+	windowEnd :=
+		windowBegin + windowSize + delta // for odd numbers of k we need to adjust wnd sz +1
+
+	if windowEnd > rightLimit {
+		windowBegin -= 2 * (windowEnd - rightLimit)
+		windowEnd = rightLimit
+		windowSize = windowEnd - windowBegin - delta
+	}
+
+	endCycle := false
+	for !endCycle {
+		if windowBegin <= leftLimit {
+			windowBegin = leftLimit
+			endCycle = true
+		}
+
+		localMaxFruits := calcFruitySliceSum(windowBegin, windowEnd)
+		if localMaxFruits > maxFruits {
+			maxFruits = localMaxFruits
+		}
+
+		windowSize++
+		windowEnd--
+		windowBegin = windowEnd - windowSize - delta
+	}
+
+	*presult = maxFruits
+	pwg.Done()
+}
+
+func fromLeftToRight(fruityPrefix []int, startPos int, k int, leftLimit int, rightLimit int) int {
+	calcFruitySliceSum := func(begin int, end int) int {
+		begin--
+		if begin < 0 {
+			return fruityPrefix[end]
+		}
+
+		return fruityPrefix[end] - fruityPrefix[begin]
+	}
+
+	maxFruits := calcFruitySliceSum(leftLimit, startPos)
+
+	windowSize := k / 2
+	delta := k - windowSize*2
+	windowEnd := startPos + delta
+	windowBegin := windowEnd - windowSize - delta
+
+	if windowBegin < leftLimit {
+		windowEnd += 2 * (leftLimit - windowBegin)
+		windowBegin = leftLimit
+		windowSize = windowEnd - delta - windowBegin
+	}
+
+	endCycle := false
+	for !endCycle {
+		if windowEnd >= rightLimit {
+			windowEnd = rightLimit
+			endCycle = true
+		}
+
+		localMaxFruits := calcFruitySliceSum(windowBegin, windowEnd)
+		if localMaxFruits > maxFruits {
+			maxFruits = localMaxFruits
+		}
+
+		windowSize++
+		windowBegin++
+		windowEnd = windowBegin + windowSize + delta
+	}
+
+	return maxFruits
+}
+
 func MaxTotalFruits(fruits [][]int, startPos int, k int) int {
 	if len(fruits) == 0 || k < 0 {
 		return 0
@@ -46,79 +137,19 @@ func MaxTotalFruits(fruits [][]int, startPos int, k int) int {
 	}
 	//fmt.Println("rightLimit = ", rightLimit)
 
-	windowSize := k / 2
+	maxFruits := 0
 
-	calcFruitySliceSum := func(begin int, end int) int {
+	wg := new(sync.WaitGroup)
-		begin--
+	wg.Add(1)
-		if begin < 0 {
-			return fruityPrefix[end]
-		}
 
-		return fruityPrefix[end] - fruityPrefix[begin]
+	go fromRightToLeft(fruityPrefix, startPos, k, leftLimit, rightLimit, wg, &maxFruits)
-	}
+	alternativeMaxFruits := fromLeftToRight(fruityPrefix, startPos, k, leftLimit, rightLimit)
 
-	maxFruits := calcFruitySliceSum(startPos, rightLimit)
+	wg.Wait()
-
-	delta := k - windowSize*2
-	windowBegin :=
-		startPos - delta // in case number of steps cannot be fully divided by 2, start position is shifted 1 position to the left
-	windowEnd :=
-		windowBegin + windowSize + (k - windowSize*2) // for odd numbers of k we need to adjust wnd sz +1
-
-	if windowEnd > rightLimit {
-		windowBegin -= 2 * (windowEnd - rightLimit)
-		windowEnd = rightLimit
-		windowSize = windowEnd - windowBegin - (k - windowSize*2)
-	}
-
-	endCycle := false
-	for !endCycle {
-		if windowBegin <= leftLimit {
-			windowBegin = leftLimit
-			endCycle = true
-		}
-
-		localMaxFruits := calcFruitySliceSum(windowBegin, windowEnd)
-		if localMaxFruits > maxFruits {
-			maxFruits = localMaxFruits
-		}
-
-		windowSize++
-		windowEnd--
-		windowBegin = windowEnd - windowSize - delta
-	}
-
-	alternativeMaxFruits := calcFruitySliceSum(leftLimit, startPos)
-	if alternativeMaxFruits > maxFruits {
-		maxFruits = alternativeMaxFruits
-	}
-
-	windowSize = k / 2
-	windowEnd = startPos + (k - windowSize*2)
-	windowBegin = windowEnd - windowSize - (k - windowSize*2)
-
-	if windowBegin < leftLimit {
-		windowEnd += 2 * (leftLimit - windowBegin)
-		windowBegin = leftLimit
-		windowSize = windowEnd - (k - windowSize*2) - windowBegin
-	}
-
-	endCycle = false
-	for !endCycle {
-		if windowEnd >= rightLimit {
-			windowEnd = rightLimit
-			endCycle = true
-		}
-
-		localMaxFruits := calcFruitySliceSum(windowBegin, windowEnd)
-		if localMaxFruits > maxFruits {
-			maxFruits = localMaxFruits
-		}
-
-		windowSize++
-		windowBegin++
-		windowEnd = windowBegin + windowSize + delta
-	}
 
+	if maxFruits > alternativeMaxFruits {
 		return maxFruits
 	}
+
+	return alternativeMaxFruits
+}