Add 3sum problem

TOC.md

@@ -76,7 +76,7 @@
 - [Next Greater for Every Element in an Array](src/_Problems_/next-greater-element)
 - [Compose Largest Number](src/_Problems_/compose-largest-number)
 - [Rotate Image](src/_Problems_/rotate-image)
-
+- [3 Sum](src/_Problems_/3Sum/)
 ### Searching
 
 - [Binary Search](src/_Searching_/BinarySearch)

src/_Problems_/3Sum/3sum.js

@@ -0,0 +1,39 @@
+const threeSum = function(nums) {
+    // sort the array
+    nums = nums.sort((a, b) => a - b);
+
+    let result = [];
+    // iterate through the array and use two pointers to find the sum
+    for (let i = 0; i < nums.length; ++i) {
+        let left = i + 1;
+        let right = nums.length - 1;
+        while (left < right) {
+            let sum = nums[i] + nums[left] + nums[right];
+            if (sum == 0) {
+                result.push([nums[i], nums[left], nums[right]]);
+                left++;
+                right--;
+            }
+            else if (sum < 0) {
+                left++;
+            }
+            else {
+                right--;
+            }
+        }
+        // skip duplicates
+        while (i < nums.length - 1 && nums[i] == nums[i + 1]) {
+            i++;
+        }
+    }
+
+    // initialize set to remove duplicate 
+    const set = new Set(result.map(JSON.stringify));
+    // final output array
+    output = (new Array(...set).map(JSON.parse));
+    return output;
+};
+
+
+module.exports = threeSum;
+

src/_Problems_/3Sum/3sum.test.js

@@ -0,0 +1,19 @@
+const threeSum = require("./3sum");
+
+describe("threeSum", () => {
+    it("Should return [[-1, -1, 2], [-1, 0, 1]]", () => {
+        expect(threeSum([-1, 0, 1, 2, -1, -4])).toEqual([
+            [-1, -1, 2],
+            [-1, 0, 1],
+        ]);
+    });
+
+    it("Should return [[0, 0, 0]]", () => {
+        expect(threeSum([0, 0, 0])).toEqual([[0, 0, 0]]);
+    });
+
+    it("Should return [[-1, -1, 2]]", () => {
+        expect(threeSum([-1, 2, -1, -4])).toEqual([[-1, -1, 2]]);
+    });
+
+});