Add mode function to mathx package (#184)

mathx/compare.go

@@ -1,9 +1,32 @@
 package mathx
 
+import "errors"
+
 // Min returns the minimum of two ints.
 func Min(a, b int) int {
 	if a < b {
 		return a
 	}
 	return b
 }
+
+// Mode returns the mode of a slice.
+func Mode(slice []int64) (int64, error) {
+	if len(slice) == 0 {
+		return 0, errors.New("invalid slice")
+	}
+
+	counts := make(map[int64]int64)
+	var mode int64
+	var maxCount int64
+
+	for _, v := range slice {
+		counts[v]++
+		if counts[v] > maxCount {
+			maxCount = counts[v]
+			mode = v
+		}
+	}
+
+	return mode, nil
+}

mathx/compare_test.go

@@ -1,6 +1,8 @@
 package mathx
 
-import "testing"
+import (
+	"testing"
+)
 
 func TestMin(t *testing.T) {
 	tests := []struct {
@@ -50,3 +52,43 @@ func TestMin(t *testing.T) {
 		})
 	}
 }
+
+func TestMode(t *testing.T) {
+	tests := []struct {
+		name    string
+		slice   []int64
+		want    int64
+		wantErr bool
+	}{
+		{
+			name:    "empty",
+			slice:   []int64{},
+			want:    0,
+			wantErr: true,
+		},
+		{
+			name:    "single",
+			slice:   []int64{1, 2, 1, 3},
+			want:    1,
+			wantErr: false,
+		},
+		{
+			name:    "multiple",
+			slice:   []int64{1, 2, 3, 1, 2},
+			want:    1,
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Mode(tt.slice)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Mode() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != tt.want {
+				t.Errorf("Mode() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}