Add three sum solution

Author: hyunjung-choi

3sum/hyunjung-choi.kt

@@ -0,0 +1,35 @@
+class Solution {
+    fun threeSum(nums: IntArray): List<List<Int>> {
+        if (nums.size < 3) return emptyList()
+
+        val result = mutableSetOf<List<Int>>()
+
+        nums.sort()
+
+        for (i in 0 until nums.size - 2) {
+
+            if (i > 0 && nums[i] == nums[i - 1]) continue
+
+            var left = i + 1
+            var right = nums.size - 1
+
+            while (left < right) {
+                val sum = nums[i] + nums[left] + nums[right]
+
+                when {
+                    sum == 0 -> {
+                        result.add(listOf(nums[i], nums[left], nums[right]))
+
+                        left++
+                        right--
+                    }
+
+                    sum < 0 -> left++
+                    else -> right--
+                }
+            }
+        }
+
+        return result.toList()
+    }
+}