feat: prefix-sum-range added to leetcode problems along with test case

apps/leet-code/src/problems/prefix-sum-range.ts

@@ -0,0 +1,38 @@
+export class NumArray
+{
+    Inums: number[];
+    PrefixSum: number[] = [];
+    constructor ( nums: number[] )
+    {
+        this.Inums = [ ...nums ];
+        for ( let i = 0; i < nums.length; i++ ) {
+            if ( i === 0 ) {
+                this.PrefixSum[ i ] = nums[ i ];
+            } else {
+                this.PrefixSum[ i ] = nums[ i ] + nums[ i - 1 ];
+            }
+        }
+    }
+
+    sumRange ( left: number, right: number ): number
+    {
+        if ( left < 0 ) {
+            throw new Error( "Bad Starting Index Range" );
+        }
+
+        if ( right > this.Inums.length ) {
+            throw new Error( "Bad Ending Index Range" );
+        }
+        let sumRange = 0;
+        for ( let i = left; i <= right; i++ ) {
+            sumRange += this.PrefixSum[ i ];
+        }
+        return sumRange;
+    }
+}
+
+/**
+ * Your NumArray object will be instantiated and called as such:
+ * var obj = new NumArray(nums)
+ * var param_1 = obj.sumRange(left,right)
+ */

apps/leet-code/src/specs/prefix-sum-range.spec.ts

@@ -0,0 +1,11 @@
+import { NumArray } from '../problems/prefix-sum-range';
+
+describe( 'Sum of Cumulative Total in Range', () =>
+{
+    it( 'should print 40 if the cumulative sum is checked from range from 1 to 4 in the array provided', () =>
+    {
+        expect( new NumArray( [ 1, 4, 5, 6, 9 ] ).sumRange( 1, 4 ) ).toBe(
+            40
+        );
+    } );
+} );