add max sum subvector - scanning algorithm

Author: LuigiAndrea

column7-back-envelope/square-root-perf/square-root_test.go

@@ -9,7 +9,7 @@ import (
 	goth "github.com/LuigiAndrea/test-helper/messages"
 )
 
-var steps int = 1000000000
+var steps int = 10000000
 
 func TestCallSquareRoot(t *testing.T) {
 	defer utilities.Elapse(goth.GetFuncName(squareRoot))()

column8-algo-design/maximum-sum-contiguous-subvector/README.md

@@ -0,0 +1 @@
+The input is a vector x of n floating-point numbers; the output is the maximum sum found in any contiguous subvector of the input. When all inputs are negative the maximum sub-vector is the empty vector, which has sum zero

column8-algo-design/maximum-sum-contiguous-subvector/scanning-algo.go

@@ -0,0 +1,14 @@
+package maxsubvector
+
+import "github.com/LuigiAndrea/GoPearls/utilities"
+
+func maxSubvector(vector []float64) (maxsofar float64) {
+	n := len(vector)
+	maxFromZeroToHere := 0.0
+	for i := 0; i < n; i++ {
+		maxFromZeroToHere = utilities.Max(maxFromZeroToHere+vector[i], 0)
+		maxsofar = utilities.Max(maxsofar, maxFromZeroToHere)
+	}
+
+	return
+}

column8-algo-design/maximum-sum-contiguous-subvector/scanning-algo_test.go

@@ -0,0 +1,33 @@
+// +build all column8 maxsubvector
+
+package maxsubvector
+
+import (
+	"testing"
+
+	a "github.com/LuigiAndrea/test-helper/assertions"
+	m "github.com/LuigiAndrea/test-helper/messages"
+)
+
+type testData struct {
+	vector        []float64
+	expectedValue float64
+}
+
+func TestMaxSubVector(t *testing.T) {
+
+	tests := []testData{
+		testData{vector: []float64{-2.4, 8, 3.3, -5.1, 2, -13}, expectedValue: 11.3},
+		testData{vector: []float64{-2.4, -5.1, -13}, expectedValue: 0},
+		testData{vector: []float64{2.4, -5.1, 13}, expectedValue: 13},
+		testData{vector: []float64{2.4, -1.1, 13}, expectedValue: 14.3},
+		testData{vector: []float64{}, expectedValue: 0},
+		testData{vector: nil, expectedValue: 0},
+	}
+
+	for i, test := range tests {
+		if err := a.AssertDeepEqual(test.expectedValue, maxSubvector(test.vector)); err != nil {
+			t.Error(m.ErrorMessageTestCount(i+1, err))
+		}
+	}
+}

utilities/helper.go

@@ -37,3 +37,14 @@ func Elapse(name string) func() {
 		fmt.Printf("%s took %v\n", name, time.Since(start))
 	}
 }
+
+//Max calculate the max element in the parameters list
+func Max(elements ...float64) float64 {
+	maxElement := 0.0
+	for _, el := range elements {
+		if el > maxElement {
+			maxElement = el
+		}
+	}
+	return maxElement
+}