diff --git a/problems/smallest-range-i/smallest_range_i.go b/problems/smallest-range-i/smallest_range_i.go
index 374be90b9..3e1a88f50 100644
--- a/problems/smallest-range-i/smallest_range_i.go
+++ b/problems/smallest-range-i/smallest_range_i.go
@@ -1 +1,17 @@
 package smallest_range_i
+
+func smallestRangeI(A []int, K int) int {
+	min, max := A[0], A[0]
+	for _, v := range A {
+		if v < min {
+			min = v
+		} else if v > max {
+			max = v
+		}
+	}
+	ans := max - min - 2*K
+	if ans < 0 {
+		return 0
+	}
+	return ans
+}
diff --git a/problems/smallest-range-i/smallest_range_i_test.go b/problems/smallest-range-i/smallest_range_i_test.go
index 374be90b9..0b0a637cc 100644
--- a/problems/smallest-range-i/smallest_range_i_test.go
+++ b/problems/smallest-range-i/smallest_range_i_test.go
@@ -1 +1,45 @@
 package smallest_range_i
+
+import "testing"
+
+type caseType struct {
+	input    []int
+	k        int
+	expected int
+}
+
+func TestSmallestRangeI(t *testing.T) {
+	tests := [...]caseType{
+		{
+			input:    []int{1},
+			k:        0,
+			expected: 0,
+		},
+		{
+			input:    []int{0, 10},
+			k:        2,
+			expected: 6,
+		},
+		{
+			input:    []int{1, 3, 6},
+			k:        3,
+			expected: 0,
+		},
+		{
+			input:    []int{1, 3, 5, 7, 9},
+			k:        1,
+			expected: 6,
+		},
+		{
+			input:    []int{18, 16, 12, 7, 9, 3, 5},
+			k:        6,
+			expected: 3,
+		},
+	}
+	for _, tc := range tests {
+		output := smallestRangeI(tc.input, tc.k)
+		if output != tc.expected {
+			t.Fatalf("input: %v, output: %v, expected: %v", tc.input, output, tc.expected)
+		}
+	}
+}