Add 3sum solution in TypeScript

Author: Jeehay28

3sum/Jeehay28.ts

@@ -0,0 +1,101 @@
+// Approach 3
+// 🗓️ 2025-04-12
+// ⏳ Time Complexity: O(n log n) + O(n^2) = O(n^2)
+// 💾 Space Complexity: O(1) (excluding output)
+
+function threeSum(nums: number[]): number[][] {
+
+    nums.sort((a, b) => a - b); // O(n log n)
+    let result: number[][] = [];
+
+    for (let i = 0; i < nums.length; i++) {
+
+        if (i > 0 && nums[i - 1] == nums[i]) continue; // skip duplicate i
+
+        let low = i + 1, high = nums.length - 1;
+        // two-pointer scan (low and high) -> takes up to O(n) time per iteration
+        while (low < high) {
+            const threeSum = nums[i] + nums[low] + nums[high];
+            if (threeSum < 0) {
+                low += 1;
+            } else if (threeSum > 0) {
+                high -= 1;
+            } else {
+                result.push([nums[i], nums[low], nums[high]]);
+
+                while (low < high && nums[low] === nums[low + 1]) low += 1 // skip duplicate low
+                while (low < high && nums[high] === nums[high - 1]) high -= 1 // skip duplicate high
+
+                low += 1;
+                high -= 1;
+
+            }
+        }
+    }
+    return result
+}
+
+
+// Approach 2
+// 🗓️ 2025-04-11
+// ❌ Time Limit Exceeded 313 / 314 testcases passed
+// ⏳ Time Complexity: O(n^2)
+// 💾 Space Complexity: O(n^2)
+
+// function threeSum(nums: number[]): number[][] {
+//   const result: number[][] = [];
+//   const triplets = new Set<string>();
+
+//   for (let i = 0; i < nums.length - 2; i++) {
+//     const seen = new Set<number>();
+//     for (let j = i + 1; j < nums.length; j++) {
+//       const twoSum = nums[i] + nums[j];
+//       if (seen.has(-twoSum)) {
+//         const triplet = [nums[i], nums[j], -twoSum].sort((a, b) => a - b); // O(log 3) = O(1)
+//         const key = triplet.join(",");
+//         if (!triplets.has(key)) {
+//           triplets.add(key);
+//           result.push(triplet);
+//         }
+//       }
+//       seen.add(nums[j]);
+//     }
+//   }
+//   return result;
+// }
+
+
+// Approach 1
+// 🗓️ 2025-04-11
+// ❌ Time Limit Exceeded!
+// ⏳ Time Complexity: O(n^3)
+// 💾 Space Complexity: O(n^2)
+
+// function threeSum(nums: number[]): number[][] {
+
+//     let triplets = new Set<string>();
+//     let result: number[][] = [];
+
+//     // const set = new Set();
+//     // set.add([1, 2, 3]);
+//     // set.add([1, 2, 3]);
+//     // console.log(set); // contains BOTH arrays
+//     // Set(2) { [ 1, 2, 3 ], [ 1, 2, 3 ] }
+
+//     for (let i = 0; i < nums.length - 2; i++) {
+//         for (let j = i + 1; j < nums.length - 1; j++) {
+//             for (let k = j + 1; k < nums.length; k++) {
+//                 if (nums[i] + nums[j] + nums[k] === 0) {
+//                     const triplet = [nums[i], nums[j], nums[k]].sort((a, b) => a - b);
+//                     const key = triplet.join(",");
+//                     if (!triplets.has(key)) {
+//                         triplets.add(key);
+//                         result.push(triplet)
+//                     }
+//                 }
+//             }
+//         }
+//     }
+
+//     return result;
+// };