slices: add Difference function

Signed-off-by: cui fliter <[email protected]>

Author: cuishuang

slices/slices.go

@@ -256,3 +256,25 @@ func Grow[S ~[]E, E any](s S, n int) S {
 func Clip[S ~[]E, E any](s S) S {
 	return s[:len(s):len(s)]
 }
+
+// Difference finds elements that exist in slice 1 but not in slice 2, and there may be duplicate elements in the returned slice.
+func Difference[E comparable](s1, s2 []E) []E {
+	var result []E
+	s2len := len(s2)
+	s1len := len(s1)
+	if s2len == 0 {
+		return s1
+	}
+	s2Map := make(map[E]bool, s2len)
+	for i := 0; i < s2len; i++ {
+		el := s2[i]
+		s2Map[el] = true
+	}
+	for i := 0; i < s1len; i++ {
+		element := s1[i]
+		if _, ok := s2Map[element]; !ok {
+			result = append(result, element)
+		}
+	}
+	return result
+}

slices/slices_test.go

@@ -767,3 +767,80 @@ func BenchmarkReplace(b *testing.B) {
 	}
 
 }
+
+func TestDifference(t *testing.T) {
+	intTypeCases := []struct {
+		name string
+		s, v []int
+		want []int
+	}{
+		{
+			name: "empty first slice",
+			s:    []int{},
+			v:    []int{1, 4},
+			want: []int{},
+		},
+		{
+			name: "empty second slice",
+			s:    []int{1, 3},
+			v:    []int{},
+			want: []int{1, 3},
+		},
+		{
+			name: "duplicates int",
+			s:    []int{2, 4, 1, 2},
+			v:    []int{1, 3, 1},
+			want: []int{2, 4, 2},
+		},
+		{
+			name: "regular use",
+			s:    []int{1, 2, 3},
+			v:    []int{3, 4, 5},
+			want: []int{1, 2},
+		},
+		{
+			name: "nil value",
+			s:    nil,
+			v:    nil,
+			want: nil,
+		},
+		{
+			name: "different size",
+			s:    []int{1, 5},
+			v:    []int{5, 10, 25},
+			want: []int{1},
+		},
+	}
+	strTypeCases := []struct {
+		name string
+		s, v []string
+		want []string
+	}{
+		{
+			name: "duplicates string",
+			s:    []string{"a", "b", "c"},
+			v:    []string{"b", "b", "z"},
+			want: []string{"a", "c"},
+		},
+		{
+			name: "contain substring",
+			s:    []string{"abc", "h", "i"},
+			v:    []string{"ab", "g", "z"},
+			want: []string{"abc", "h", "i"},
+		},
+	}
+	for _, test := range intTypeCases {
+		t.Run(test.name, func(tt *testing.T) {
+			if got := Difference(test.s, test.v); !Equal(got, test.want) {
+				tt.Errorf("Difference(%v) = %v, want %v", test.s, got, test.want)
+			}
+		})
+	}
+	for _, test := range strTypeCases {
+		t.Run(test.name, func(tt *testing.T) {
+			if got := Difference(test.s, test.v); !Equal(got, test.want) {
+				tt.Errorf("Difference(%v) = %v, want %v", test.s, got, test.want)
+			}
+		})
+	}
+}