feat: add 3Sum

Author: dukeluo

README.md

@@ -17,3 +17,4 @@ https://neetcode.io/roadmap
 | 128 | [Longest Consecutive Sequence](https://leetcode.com/problems/longest-consecutive-sequence/)           | Medium     | [TypeScript](./TypeScript/128.longest-consecutive-sequence.ts)     | Arrays & Hashing |
 | 125 | [Valid Palindrome](https://leetcode.com/problems/valid-palindrome/)                                   | Easy       | [TypeScript](./TypeScript/125.valid-palindrome.ts)                 | Two Pointers     |
 | 167 | [Two Sum II - Input Array Is Sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/) | Medium     | [TypeScript](./TypeScript/167.two-sum-ii-input-array-is-sorted.ts) | Two Pointers     |
+| 15  | [3Sum](https://leetcode.com/problems/3sum/)                                                           | Medium     | [TypeScript](./TypeScript/15.3sum.ts)                              | Two Pointers     |

TypeScript/15.3sum.ts

@@ -0,0 +1,29 @@
+function threeSum(nums: number[]): number[][] {
+  const result: number[][] = [];
+  nums.sort((a, b) => a - b);
+
+  for (let i = 0; i < nums.length - 2; i++) {
+    if (nums[i] > 0) break;
+    if (nums[i] === nums[i - 1]) continue;
+
+    let l = i + 1;
+    let r = nums.length - 1;
+
+    while (l < r) {
+      const sum = nums[i] + nums[l] + nums[r];
+
+      if (sum === 0) {
+        result.push([nums[i], nums[l], nums[r]]);
+        r -= 1;
+        l += 1;
+        while (nums[l] === nums[l - 1]) l++;
+      } else if (sum > 0) {
+        r--;
+      } else {
+        l++;
+      }
+    }
+  }
+
+  return result;
+}