clojure: partition equal subset sum

Author: PoorlyDefinedBehaviour

clojure/algorithms/others/partition-equal-subset-sum-april-8-2024/main.clj

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+(ns core
+  (:require [clojure.test :refer [deftest is testing]]))
+
+(comment
+  "Given an integer array nums, return true if
+you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise.
+   
+Example 1:
+
+Input: nums = [1,5,11,5]
+Output: true
+Explanation: The array can be partitioned as [1, 5, 5] and [11].
+Example 2:
+
+Input: nums = [1,2,3,5]
+Output: false
+Explanation: The array cannot be partitioned into equal sum subsets.
+ 
+
+Constraints:
+
+1 <= nums.length <= 200
+1 <= nums[i] <= 100")
+
+;; time O(n * sum(nums))
+;; space O(sum(nums))
+(defn can-partition [nums]
+  ;; O(n)
+  (let [sum (reduce + nums)
+        half (/ sum 2)]
+    (if (odd? sum)
+      false
+      ;; O(n)
+      (let [result (reduce (fn [seen num]
+                             ;; O(sum(nums))
+                             (let [new-seen (reduce (fn [new-seen other-num] (let [total (+ num other-num)]
+                                                                               (if (<= half total)
+                                                                                 (conj new-seen total)
+                                                                                 new-seen)))
+                                                    seen
+                                                    seen)]
+                               (if (contains? new-seen half)
+                                 (reduced true)
+                                 new-seen)))
+                           #{0}
+                           nums)]
+        (= result true)))))
+
+(deftest can-partition-test
+  (testing "example 1"
+    (is (= true (can-partition '(1 5 11 5))))
+    (is (= false (can-partition '(1 2 3 5))))
+    (is (= true (can-partition '(1 1))))))
+
+(clojure.test/run-all-tests)