Solution to 1027

Author: Indigo2233

src/unresolved/1027.longest-arithmetic-subsequence.jl renamed to src/problems/1027.longest-arithmetic-subsequence.jl

@@ -1,8 +1,8 @@
 # ---
 # title: 1027. Longest Arithmetic Subsequence
 # id: problem1027
-# author: Tian Jun
-# date: 2020-10-31
+# author: Indigo
+# date: 2022-04-14
 # difficulty: Medium
 # categories: Dynamic Programming
 # link: <https://leetcode.com/problems/longest-arithmetic-subsequence/description/>
@@ -60,5 +60,16 @@
 ## @lc code=start
 using LeetCode
 
-## add your code here:
+function longest_arith_seq_length(nums::Vector{Int})
+    len = length(nums)
+    len == 1 && return 0
+    dp = fill(0, len, 1001)
+    res = 0
+    for i in 1:len, j in 1:(i - 1)
+        d = nums[i] - nums[j] + 501
+        dp[i, d] = max(dp[i, d], dp[j, d] + 1)
+        res = max(res, dp[i, d])
+    end
+    return res + 1
+end
 ## @lc code=end

test/problems/1027.longest-arithmetic-subsequence.jl

@@ -0,0 +1,6 @@
+@testset "1027.longest-arithmetic-subsequence.jl" begin
+    @test longest_arith_seq_length([20, 1, 15, 3, 10, 5, 8]) == 4
+    @test longest_arith_seq_length([3, 6, 9, 12]) == 4
+    @test longest_arith_seq_length([9, 4, 7, 2, 10]) == 3
+    @test longest_arith_seq_length([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) == 10
+end