add 3Sum solution

Author: HoonDongKang

3sum/HoonDongKang.ts

@@ -0,0 +1,39 @@
+/**
+ * [Problem]: [15] 3Sum
+ * (https://leetcode.com/problems/3sum/description/)
+ */
+
+function threeSum(nums: number[]): number[][] {
+    //시간 복잡도: O(n^2)
+    //공간 복잡도: O(1)
+    function pointerFunc(nums: number[]): number[][] {
+        const result: number[][] = [];
+        nums.sort((a, b) => a - b);
+
+        for (let i = 0; i < nums.length; i++) {
+            if (i > 0 && nums[i] === nums[i - 1]) continue;
+            let left = i + 1;
+            let right = nums.length - 1;
+
+            while (left < right) {
+                const sum = nums[i] + nums[left] + nums[right];
+                if (sum === 0) {
+                    result.push([nums[i], nums[left], nums[right]]);
+
+                    while (left < right && nums[left] === nums[left + 1]) left++;
+                    while (left < right && nums[right] === nums[right - 1]) right--;
+
+                    left++;
+                    right--;
+                } else if (sum < 0) {
+                    left++;
+                } else {
+                    right--;
+                }
+            }
+        }
+        return result;
+    }
+
+    return pointerFunc(nums);
+}