Create 0446-arithmetic-slices-ii-subsequence.kt

Author: a93a

kotlin/0446-arithmetic-slices-ii-subsequence.kt

@@ -0,0 +1,49 @@
+// dp
+class Solution {
+    fun numberOfArithmeticSlices(nums: IntArray): Int {
+        var res = 0
+        val dp = HashMap<Pair<Int, Long>, Int>()
+
+        for (i in 0 until nums.size) {
+            for (j in 0 until i) {
+                val d = nums[i].toLong() - nums[j]
+                dp[i to d] = (dp[i to d] ?: 0) + 1 + (dp[j to d] ?: 0)
+                res += (dp[j to d] ?: 0)
+            }
+        }
+
+        return res
+    }
+}
+
+// recursion + memoization
+class Solution {
+    fun numberOfArithmeticSlices(nums: IntArray): Int {
+        val dp = HashMap<String, Int>()
+        val count = HashMap<Long, MutableList<Int>>()
+
+        nums.forEachIndexed { i, n ->
+            count.getOrPut(n.toLong()) { mutableListOf() }.apply { add(i) }
+        }
+        
+        fun dfs(i: Int, d: Long, s: Int): Int {
+            dp["$i:$d:$s"]?.let { return it }
+
+            var res = if (s > 2) 1 else 0
+            count[nums[i] + d]?.forEach { j ->
+                if (j > i) res += dfs(j, d, s + 1)
+            }
+
+            dp["$i:$d:$s"] = res
+            return res
+        }
+
+        var res = 0
+        for (i in 0 until nums.size) {
+            for (j in i + 1 until nums.size)
+                res += dfs(j, nums[j].toLong() - nums[i], 2)
+        }
+
+        return res
+    }
+}