Create 0018-4sum.kt

Author: a93a

kotlin/0018-4sum.kt

@@ -0,0 +1,46 @@
+class Solution {
+    fun fourSum(nums: IntArray, target: Int): List<List<Int>> {
+        nums.sort()
+        val res = ArrayList<ArrayList<Int>>()
+        val temp = ArrayList<Int>()
+
+        fun kSum(k: Int, start: Int, targetSum: Long) {
+            if (k != 2) {
+                for (i in start..(nums.size - k)) {
+                    if (i > start && nums[i - 1] == nums[i])
+                        continue 
+                    
+                    temp.add(0, nums[i])
+                    kSum(k - 1, i + 1, targetSum - nums[i])
+                    temp.removeAt(0)
+                }
+
+                return
+            }
+            
+            var left = start
+            var right = nums.lastIndex
+            while (left < right) {       
+                val sum = nums[left].toLong() + nums[right].toLong()
+                if (sum < targetSum) {
+                    left++
+                } else if (sum > targetSum) {
+                    right--
+                } else {
+                    temp.add(0, nums[left])
+                    temp.add(0, nums[right])
+                    res.add(ArrayList(temp))
+                    temp.removeAt(0)
+                    temp.removeAt(0)
+                    
+                    left++
+                    while (left < right && nums[left - 1] == nums[left])
+                        left++
+                }
+            }
+        }
+
+        kSum(4, 0, target.toLong())
+        return res
+    }
+}