Range sum query- Immutable

Author: volodimyr

303.range_sum_query_immutable/range_sum.go

@@ -0,0 +1,58 @@
+// 303. Range sum query- Immutable
+// Topics: 'Array', 'Design', 'Prefix Sum'
+
+// Given an integer array nums, handle multiple queries of the following type:
+
+//     Calculate the sum of the elements of nums between indices left and right inclusive where left <= right.
+
+// Implement the NumArray class:
+
+//     NumArray(int[] nums) Initializes the object with the integer array nums.
+//     int sumRange(int left, int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]).
+
+// Example 1:
+
+// Input
+// ["NumArray", "sumRange", "sumRange", "sumRange"]
+// [[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]
+// Output
+// [null, 1, -1, -3]
+
+// Explanation
+// NumArray numArray = new NumArray([-2, 0, 3, -5, 2, -1]);
+// numArray.sumRange(0, 2); // return (-2) + 0 + 3 = 1
+// numArray.sumRange(2, 5); // return 3 + (-5) + 2 + (-1) = -1
+// numArray.sumRange(0, 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3
+
+// Constraints:
+
+//     1 <= nums.length <= 104
+//     -105 <= nums[i] <= 105
+//     0 <= left <= right < nums.length
+//     At most 104 calls will be made to sumRange.
+
+package rangesumqueryimmutable
+
+type NumArray struct {
+	prefix []int
+	nums   []int
+}
+
+func Constructor(nums []int) NumArray {
+	var prefix []int
+	var sum int
+	for _, num := range nums {
+		sum += num
+		prefix = append(prefix, sum)
+	}
+	return NumArray{prefix: prefix, nums: nums}
+}
+
+func (n *NumArray) SumRange(left int, right int) int {
+	sum := n.prefix[right]
+	if left == 0 {
+		return sum
+	}
+	sum -= n.prefix[left-1]
+	return sum
+}

303.range_sum_query_immutable/range_sum_test.go

@@ -0,0 +1,127 @@
+package rangesumqueryimmutable
+
+import "testing"
+
+func TestNumArray(t *testing.T) {
+	tests := []struct {
+		name    string
+		nums    []int
+		queries []struct {
+			left  int
+			right int
+			want  int
+		}
+	}{
+		{
+			name: "example case",
+			nums: []int{-2, 0, 3, -5, 2, -1},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 2, 1},
+				{2, 5, -1},
+				{0, 5, -3},
+			},
+		},
+		{
+			name: "single element",
+			nums: []int{5},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 0, 5},
+			},
+		},
+		{
+			name: "all positive numbers",
+			nums: []int{1, 2, 3, 4, 5},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 4, 15},
+				{1, 3, 9},
+				{2, 2, 3},
+			},
+		},
+		{
+			name: "all negative numbers",
+			nums: []int{-1, -2, -3, -4, -5},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 4, -15},
+				{1, 3, -9},
+				{3, 4, -9},
+			},
+		},
+		{
+			name: "zeros",
+			nums: []int{0, 0, 0, 0},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 3, 0},
+				{1, 2, 0},
+			},
+		},
+		{
+			name: "left equals right",
+			nums: []int{10, 20, 30, 40},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 0, 10},
+				{2, 2, 30},
+				{3, 3, 40},
+			},
+		},
+		{
+			name: "full range",
+			nums: []int{1, 2, 3},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 2, 6},
+			},
+		},
+		{
+			name: "mixed positive and negative",
+			nums: []int{5, -3, 4, -1, 2},
+			queries: []struct {
+				left  int
+				right int
+				want  int
+			}{
+				{0, 1, 2},
+				{1, 3, 0},
+				{2, 4, 5},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			numArray := Constructor(tt.nums)
+			for i, q := range tt.queries {
+				got := numArray.SumRange(q.left, q.right)
+				if got != q.want {
+					t.Errorf("query %d: SumRange(%d, %d) = %d, want %d", i, q.left, q.right, got, q.want)
+				}
+			}
+		})
+	}
+}