From 6269b9b896eefe51acfa860e87a111f40430cdeb Mon Sep 17 00:00:00 2001
From: Seongbeom Park <sparkamita90@gmail.com>
Date: Sun, 24 Apr 2022 05:37:10 +0900
Subject: [PATCH] memoization and early termination

Verifying solution...
Test 1 passed!
Test 2 passed!
Test 3 failed  [Hidden]
Test 4 passed! [Hidden]
Test 5 failed  [Hidden]
---
 extra/distract-the-trainers/solution.py | 36 ++++++++++++-------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/extra/distract-the-trainers/solution.py b/extra/distract-the-trainers/solution.py
index 0d12d81..356cf68 100644
--- a/extra/distract-the-trainers/solution.py
+++ b/extra/distract-the-trainers/solution.py
@@ -1,12 +1,15 @@
 def solution(banana_list):
     fewest_possible_number = len(banana_list)
+    memo = {}
     for pairs in generate_trainer_pairs(list(range(len(banana_list)))):
         possible_number = len(banana_list)
         for i, j in pairs:
-            if check_loop(banana_list[i], banana_list[j]):
+            if check_loop(banana_list[i], banana_list[j], memo):
                 possible_number -= 2
         if possible_number < fewest_possible_number:
             fewest_possible_number = possible_number
+        if fewest_possible_number < 2: # early termination
+            break
     return fewest_possible_number
 
 import copy
@@ -15,28 +18,25 @@ def generate_trainer_pairs(trainer_id_list):
         yield []
     else:
         first_id = trainer_id_list[0]
-        temp_list = copy.deepcopy(trainer_id_list)
-        temp_list.remove(first_id)
-        for second_id in temp_list:
-            tt_list = copy.deepcopy(temp_list)
-            tt_list.remove(second_id)
-            for pairs in generate_trainer_pairs(tt_list):
+        for second_id in trainer_id_list[1:]:
+            reduced_list = copy.deepcopy(trainer_id_list)
+            seduced_list.remove(first_id)
+            reduced_list.remove(second_id)
+            for pairs in generate_trainer_pairs(reduced_list):
                 yield [(first_id, second_id)] + pairs
 
-def check_loop(x, y):
-    if (x + y) % 2 == 1: # sum is odd
-        return True
-    a, b = x, y
-    memo = []
+def check_loop(a, b, memo):
+    if (a, b) in memo:
+        return memo[(a, b)]
     while a != b:
-        if a > b:
-            a, b = a - b, 2*b
-        else:
-            a, b = 2*a, b - a
-        if (a, b) in memo:
+        if (a + b) % 2 == 1: # sum is odd
+            memo[(a, b)] = True
             return True
+        if a > b:
+            a, b = (a - b)/2, b
         else:
-            memo += [(a, b)]
+            a, b = a, (b - a)/2
+    memo[(a, b)] = False
     return False
 
 tests = [