Add MinSliceIndex/MaxSliceIndex

README.md

@@ -137,6 +137,14 @@ MaxN returns the largest int in the set provided.
 If no values are provided, Max returns 0.
 
 
+## func MaxSliceIndex
+``` go
+func MaxSliceIndex(slice interface{}, less func(i, j int) bool) int
+```
+MaxSliceIndex returns the largest element index in the slice.
+If slice is empty, MaxSliceIndex returns -1
+
+
 ## func MaxUint
 ``` go
 func MaxUint(a, b uint) uint
@@ -316,6 +324,14 @@ MinN returns the smallest int in the set provided.
 If no values are provided, Min returns 0.
 
 
+## func MinSliceIndex
+``` go
+func MinSliceIndex(slice interface{}, less func(i, j int) bool) int
+```
+MinSliceIndex returns the smallest element index in the slice.
+If slice is empty, MinSliceIndex returns -1
+
+
 ## func MinUint
 ``` go
 func MinUint(a, b uint) uint

slice.go

@@ -0,0 +1,35 @@
+package math
+
+import "reflect"
+
+// MinSliceIndex returns the smallest element index in the slice.
+// If slice is empty, MinSliceIndex returns -1
+func MinSliceIndex(slice interface{}, less func(i, j int) bool) int {
+	v := reflect.ValueOf(slice)
+	if v.Len() == 0 {
+		return -1
+	}
+	minIndex := 0
+	for i := 1; i < v.Len(); i++ {
+		if less(i, minIndex) {
+			minIndex = i
+		}
+	}
+	return minIndex
+}
+
+// MaxSliceIndex returns the largest element index in the slice.
+// If slice is empty, MaxSliceIndex returns -1
+func MaxSliceIndex(slice interface{}, less func(i, j int) bool) int {
+	v := reflect.ValueOf(slice)
+	if v.Len() == 0 {
+		return -1
+	}
+	maxIndex := 0
+	for i := 1; i < v.Len(); i++ {
+		if less(maxIndex, i) {
+			maxIndex = i
+		}
+	}
+	return maxIndex
+}

slice_test.go

@@ -0,0 +1,63 @@
+package math
+
+import (
+	"testing"
+)
+
+var minSliceIndexTests = []struct {
+	v    []struct{ n int }
+	want int
+}{
+	{
+		v:    []struct{ n int }{{1}},
+		want: 0,
+	},
+	{
+		v:    []struct{ n int }{{7}, {2}},
+		want: 1,
+	},
+	{
+		v:    []struct{ n int }{{12}, {18}, {17}, {9}},
+		want: 3,
+	},
+}
+
+func TestMinSliceIndex(t *testing.T) {
+	for i, tt := range minSliceIndexTests {
+		got := MinSliceIndex(tt.v, func(i, j int) bool {
+			return tt.v[i].n < tt.v[j].n
+		})
+		if tt.want != got {
+			t.Errorf("%d: MinSliceIndex(%v) = %v, want %v", i+1, tt.v, got, tt.want)
+		}
+	}
+}
+
+var maxSliceIndexTests = []struct {
+	v    []struct{ n int }
+	want int
+}{
+	{
+		v:    []struct{ n int }{{1}},
+		want: 0,
+	},
+	{
+		v:    []struct{ n int }{{7}, {2}},
+		want: 0,
+	},
+	{
+		v:    []struct{ n int }{{12}, {18}, {17}, {19}},
+		want: 3,
+	},
+}
+
+func TestMaxSliceIndex(t *testing.T) {
+	for i, tt := range maxSliceIndexTests {
+		got := MaxSliceIndex(tt.v, func(i, j int) bool {
+			return tt.v[i].n < tt.v[j].n
+		})
+		if tt.want != got {
+			t.Errorf("%d: MaxSliceIndex(%v) = %v, want %v", i+1, tt.v, got, tt.want)
+		}
+	}
+}