[ppxyn1] WEEK 09 Solutions

linked-list-cycle/ppxyn1.py

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+# idea : -
+# Time complxity : O(n)
+
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def hasCycle(self, head: Optional[ListNode]) -> bool:
+        visited = set()
+        while head:
+            if head in visited:
+                return True
+            else:
+                visited.add(head)
+                head = head.next
+        return False
+
+# Floyd (cycle detection)
+# class Solution:
+#     def hasCycle(self, head: Optional[ListNode]) -> bool:
+#         slow, fast = head, head
+#         while fast and fast.next:
+#             slow = slow.next
+#             fast = fast.next.next
+#             if slow == fast:
+#                 return True
+#         return False
+

maximum-product-subarray/ppxyn1.py

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+#idea : DP
+# Time Complexity: O(n)
+class Solution:
+    def maxProduct(self, nums: List[int]) -> int:
+        ans = 0
+        max_prod = min_prod = nums[0]
+
+        for i in range(1, len(nums)):
+            if nums[i] < 0:
+                max_prod, min_prod = min_prod, max_prod
+            max_prod = max(nums[i], max_prod * nums[i])
+            min_prod = min(nums[i], min_prod * nums[i])
+
+            ans = max(ans, max_prod)
+
+        return ans
+
+
+# Time Complxity: O(N^2)
+# class Solution:
+#     def maxProduct(self, nums: List[int]) -> int:
+#         max_product = nums[0]
+#         for s in range(len(nums)):
+#             product = 1
+#             for e in range(s, len(nums)):
+#                 product *= nums[e]
+#                 max_product = max(product, max_product)
+#         return max_product
+
+

sum-of-two-integers/ppxyn1.py

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+# idea : -
+# Time Complexity: O(1)
+
+# Solution (1) : It feels a bit like cheating though... but passed the answer lol
+class Solution:
+    def getSum(self, a: int, b: int) -> int:
+        return sum([a, b])
+
+'''
+# Try and Error : Another way I tried is by using log.
+
+import numpy as np
+
+class Solution:
+    def getSum(self, a: int, b: int) -> int:
+        return int(np.log(np.exp(a) * np.exp(b)))
+
+Ths way has a problem that it is not calculated as log(exp(a) * exp(b)) = log(exp(a+b)) = a + b like human.
+'''
+
+