Add Find Pivot Index & Running Sum of 1d Array

Author: GolubevDS

README.MD

@@ -21,3 +21,5 @@ Solutions to problems from the [LeetCode Patterns](https://seanprashad.com/leetc
 | [Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements)                           | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/removeElements/index.js)         | Easy       |
 | [Two Sum](https://leetcode.com/problems/two-sum)                                                                   | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/twoSum/index.js)                 | Easy       |
 | [Majority Element](https://leetcode.com/problems/majority-element)                                                 | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/majorityElement/index.js)        | Easy       |
+| [Running Sum of 1d Array](https://leetcode.com/problems/running-sum-of-1d-array/)                                  | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/runningSum/index.js)             | Easy       |
+| [Find Pivot Index](https://leetcode.com/problems/find-pivot-index/)                                                | [Solution](https://github.com/GolubevDS/LeetCodePatterns/blob/main/solutions/pivotIndex/index.js)             | Easy       |

solutions/pivotIndex/README.MD

@@ -0,0 +1,9 @@
+## [724. Find Pivot Index](https://leetcode.com/problems/find-pivot-index/)
+
+Given an array of integers `nums`, calculate the pivot index of this array.
+
+The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index's right.
+
+If the index is on the left edge of the array, then the left sum is `0` because there are no elements to the left. This also applies to the right edge of the array.
+
+Return the leftmost pivot index. If no such index exists, return `-1`.

solutions/pivotIndex/index.js

@@ -0,0 +1,20 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+function pivotIndex(nums) {
+	const totalSum = nums.reduce((acc, val) => acc + val, 0);
+	let leftSum = 0;
+
+	for (let i = 0; i < nums.length; i++) {
+		if (leftSum === totalSum - leftSum - nums[i]) {
+			return i;
+		}
+
+		leftSum += nums[i];
+	}
+
+	return -1;
+}
+
+module.exports = pivotIndex;

solutions/pivotIndex/index.spec.js

@@ -0,0 +1,26 @@
+const pivotIndex = require('.');
+
+describe("Find Pivot Index", () => {
+	it("should return -1 if the input array is empty", () => {
+		const result = pivotIndex([]);
+		expect(result).toEqual(-1);
+	});
+
+	it("should return -1 if there is no pivot index", () => {
+		const input = [1, 2, 3, 4, 5];
+		const result = pivotIndex(input);
+		expect(result).toEqual(-1);
+	});
+
+	it("should return the correct pivot index if there is one", () => {
+		const input = [1, 7, 3, 6, 5, 6];
+		const result = pivotIndex(input);
+		expect(result).toEqual(3);
+	});
+
+	it("should work with arrays containing only one element", () => {
+		const input = [1];
+		const result = pivotIndex(input);
+		expect(result).toEqual(0);
+	});
+});

solutions/runningSum/README.MD

@@ -0,0 +1,5 @@
+## [1480. Running Sum of 1d Array](https://leetcode.com/problems/running-sum-of-1d-array/)
+
+Given an array `nums`. We define a running sum of an array as `runningSum[i] = sum(nums[0]…nums[i])`.
+
+Return the running sum of `nums`.

solutions/runningSum/index.js

@@ -0,0 +1,17 @@
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+function runningSum(nums) {
+	let sum = 0;
+	const result = [];
+
+	for (let i = 0; i < nums.length; i++) {
+		sum += nums[i];
+		result.push(sum);
+	}
+
+	return result;
+}
+
+module.exports = runningSum;

solutions/runningSum/index.spec.js

@@ -0,0 +1,26 @@
+const runningSum = require('.');
+
+describe('Running Sum of 1d Array', () => {
+	it('should return an empty array if given an empty array', () => {
+		const result = runningSum([]);
+		expect(result).toEqual([]);
+	});
+
+	it('should return an array with the same length as the input array', () => {
+		const input = [1, 2, 3, 4, 5];
+		const result = runningSum(input);
+		expect(result.length).toEqual(input.length);
+	});
+
+	it('should correctly calculate the running sum of the input array', () => {
+		const input = [1, 2, 3, 4, 5];
+		const result = runningSum(input);
+		expect(result).toEqual([1, 3, 6, 10, 15]);
+	});
+
+	it('should work with arrays containing negative numbers', () => {
+		const input = [-1, 2, -3, 4, -5];
+		const result = runningSum(input);
+		expect(result).toEqual([-1, 1, -2, 2, -3]);
+	});
+});