add 1027

Author: Ashwagandha-coder

contest/src/main/java/com/github/contest/Execute.kt

@@ -1,7 +1,7 @@
 package com.github.contest
 
 
-import com.github.contest.dp.longestStrChain
+import com.github.contest.dp.longestArithSeqLength
 import java.util.TreeMap
 
 
@@ -11,8 +11,7 @@ import java.util.TreeMap
 
 fun main() {
 
-    longestStrChain(arrayOf("a", "b", "ba", "bca", "bda", "bdca")).also { println(it) }
-
+    longestArithSeqLength(intArrayOf(3, 6, 9, 12))
 }
 
 fun generateTesting() {

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

@@ -395,3 +395,25 @@ fun longestStrChain(words: Array<String>): Int {
 
     return longestChain
 }
+
+/**
+ * 1027. Longest Arithmetic Subsequence
+ */
+
+fun longestArithSeqLength(nums: IntArray): Int {
+    val n = nums.size
+
+    val dp = Array(n) { mutableMapOf<Int, Int>() }
+    var longest = 2
+
+    for (i in 1 until n) {
+        for (j in 0 until i) {
+            val diff = nums[i] - nums[j]
+            val length = dp[j].getOrDefault(diff, 1) + 1
+            dp[i][diff] = length
+            longest = maxOf(longest, length)
+        }
+    }
+
+    return longest
+}