feat: Solves Three Number Sum

Author: brianr482

arrays-strings/three-number-sum.js

@@ -0,0 +1,58 @@
+/**
+ * AlgoExpert
+ * 
+ * Write a function that takes in a non-empty array of distinct integers and an
+ * integer representing a target sum. The function should find all triplets in
+ * the array that sum up to the target sum and return a two-dimensional array of
+ * all these triplets. The numbers in each triplet should be ordered in ascending
+ * order, and the triplets themselves should be ordered in ascending order with
+ * respect to the numbers they hold.
+ * 
+ * If no three numbers sum up to the target sum, the function should return an
+ * empty array.
+ */
+
+/**
+ * @param {number[]} array 
+ * @param {number} targetSum 
+ * @returns {array[][]}
+ */
+function threeNumberSum(array, targetSum) {
+  // O(n^2) time | O(n) space
+
+  // Edge case
+  if (array.length < 3) {
+		return [];
+	}
+	
+	const triplets = [];
+	array.sort((a, b) => a - b);
+	
+	const arrayLength = array.length;
+	let i = 0;
+	let l, r;
+	while (i < arrayLength - 2) {
+		const currentElement = array[i];
+		l = i + 1;
+		r = arrayLength - 1;
+		
+		while (l < r) {
+			const leftElement = array[l];
+			const rightElement = array[r];
+			const total = currentElement + leftElement + rightElement;
+			if (total === targetSum) {
+				triplets.push([currentElement, leftElement, rightElement]);
+				l++;
+				r--;
+			} else if (total > targetSum) {
+				r--;
+			} else {
+				l++;
+			}
+		}
+
+		i++;
+	}
+	
+	return triplets;
+}