add prod variant for 1027

Author: Ashwagandha-coder

contest/src/main/java/com/github/contest/dp/DpLeetcode.kt

@@ -417,3 +417,5 @@ fun longestArithSeqLength(nums: IntArray): Int {
 
     return longest
 }
+
+

contest/src/main/java/com/github/contest/dp/DpProdVariant.kt

@@ -129,4 +129,23 @@ fun longestStrChainProdVariant(words: Array<String>): Int {
         dp[word] = currentChain
         currentChain
     }
+}
+
+/**
+ * 1027. Longest Arithmetic Subsequence
+ * Prod Variant
+ */
+
+fun longestArithSeqLengthProdVariant(nums: IntArray): Int {
+    val dp = Array(nums.size) { mutableMapOf<Int, Int>() }
+    var longest = 0
+
+    return (1 until nums.size).maxOf { i ->
+        (0 until i).maxOf { j ->
+            val diff = nums[i] - nums[j]
+            val len = dp[j].getOrDefault(diff, 1) + 1
+            dp[i][diff] = len
+            len
+        }
+    }
 }