feat: add new file

Author: Ahtaxam

src/_Problems_/3Sum/3sum.js

@@ -0,0 +1,39 @@
+var 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;
+