[ayosecu] WEEK 02 solutions

3sum/ayosecu.py

@@ -0,0 +1,52 @@
+from typing import List
+
+class Solution:
+    """
+        - Algorithm
+            - Sort and compares with three pointers: target, left(l), right(r)
+        - Time Complexity: O(n^2), n = len(nums)
+            - sort : O(nlogn)
+            - nested two loops : O(n^2)
+            - O(nlogn + n^2) => O(n^2)
+        - Space Complexity: O(n^2) if result included.
+            - result size : result.append() called in n^2 times (nested two loops)
+    """
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        result = []
+        nums.sort()
+
+        n = len(nums)
+        for i in range(n - 2):
+            # skip duplicated numbers
+            if i > 0 and nums[i] == nums[i - 1]:
+                continue
+
+            target = nums[i]
+            l, r = i + 1, n - 1
+            while l < r:
+                if nums[l] + nums[r] == -target:
+                    result.append([target, nums[l], nums[r]])                   
+                    # skip duplicated numbers
+                    while l < r and nums[l] == nums[l + 1]:
+                        l += 1
+                    while l < r and nums[r] == nums[r - 1]:
+                        r -= 1
+                    l += 1
+                    r -= 1
+                elif nums[l] + nums[r] < -target:
+                    l += 1
+                else:
+                    r -= 1
+
+        return result
+
+tc = [
+        ([-1,0,1,2,-1,-4], [[-1,-1,2],[-1,0,1]]),
+        ([0,1,1], []),
+        ([0,0,0], [[0,0,0]])
+]
+
+for i, (nums, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.threeSum(nums)
+    print(f"TC {i} is Passed!" if e == r else f"TC {i} is Failed! - Expected: {e}, Result: {r}")

climbing-stairs/ayosecu.py

@@ -0,0 +1,36 @@
+class Solution:
+    """
+        - Time Complexity: O(n)
+        - Space Complexity: O(n)
+    """
+    def climbStairs(self, n: int) -> int:
+        """
+            - DP Formation
+                - dp[0] = 1
+                - dp[1] = 1
+                - dp[2] = dp[1] + dp[0] = 2
+                - dp[3] = dp[2] + dp[1] = 3
+                - dp[i] = dp[i - 1] + dp[i - 2]
+        """
+        if n <= 1:
+            return 1
+
+        dp = [1] * (n + 1)
+
+        for i in range(2, n + 1):
+            dp[i] = dp[i - 1] + dp[i - 2]
+
+        return dp[-1]
+
+
+tc = [
+        (1, 1),
+        (2, 2),
+        (3, 3),
+        (4, 5)
+]
+
+for i, (n, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.climbStairs(n)
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")

product-of-array-except-self/ayosecu.py

@@ -0,0 +1,56 @@
+from typing import List
+
+class Solution:
+    """
+        - Time Complexity: O(n), n = len(nums)
+        - Space Complexity: O(n)
+    """
+    def productExceptSelfN(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+        prefix, suffix, result = [0] * n, [0] * n, [0] * n
+
+        # Calculate prefix and suffix production
+        prefix[0], suffix[-1] = nums[0], nums[-1]
+        for i in range(1, n - 1):
+            prefix[i] = prefix[i - 1] * nums[i]
+            j = n - i - 1
+            suffix[j] = suffix[j + 1] * nums[j]
+
+        # Update the result
+        result[0], result[-1] = suffix[1], prefix[-2]
+        for i in range(1, n - 1):
+            result[i] = prefix[i - 1] * suffix[i + 1]
+
+        return result
+
+    """
+        - Time Complexity: O(n), n = len(nums)
+        - Space Complexity
+            - O(1), if output space (result) is ignored
+            - O(n), if output space (result) is considered
+    """
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+        result = [1] * n
+
+        left = 1
+        for i in range(n):
+            result[i] = left
+            left = result[i] * nums[i]
+
+        right = 1
+        for i in range(n - 1, -1, -1):
+            result[i] *= right
+            right *= nums[i]
+
+        return result
+
+tc = [
+        ([1, 2, 3, 4], [24, 12, 8, 6]),
+        ([-1, 1, 0, -3, 3], [0, 0, 9, 0, 0])
+]
+
+for i, (nums, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.productExceptSelf(nums)
+    print(f"TC {i} is Passed!" if e == r else f"TC {i} is Failed! - Expected: {e}, Result: {r}")

valid-anagram/ayosecu.py

@@ -0,0 +1,20 @@
+from collections import Counter
+
+class Solution:
+    """
+        - Time Complexity: O(n + m), n = len(s), m = len(t)
+        - Space Complexity: O(n + m)
+    """
+    def isAnagram(self, s: str, t: str) -> bool:
+        return Counter(s) == Counter(t)
+
+tc = [
+        ("anagram", "nagaram", True),
+        ("rat", "car", False),
+        ("abc", "dcba", False)
+]
+
+for i, (s, t, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.isAnagram(s, t)
+    print(f"TC {i} is Passed!" if e == r else f"TC {i} is Failed! - Expected: {e}, Result: {r}")

validate-binary-search-tree/ayosecu.py

@@ -0,0 +1,47 @@
+from typing import Optional
+
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution:
+    """
+        - Time Complexity: O(n), n = The number of nodes
+        - Space Complexity: O(H), H = The height of tree
+            - Stack size of checkVal
+            - H = logn, if the tree is balanced
+            - H = n, if the tree is skewed
+    """
+    def isValidBST(self, root: Optional[TreeNode]) -> bool:
+
+        def checkVal(node, min_val, max_val):
+            if not node:
+                return True
+
+            if node.val >= max_val or node.val <= min_val:
+                return False
+
+            return checkVal(node.left, min_val, node.val) and checkVal(node.right, node.val, max_val)
+
+        return checkVal(root, float("-inf"), float("inf"))
+
+def doTest():
+    sol = Solution()
+    root1 = TreeNode(2)
+    root1.left = TreeNode(1)
+    root1.right = TreeNode(3)
+    result1 = sol.isValidBST(root1)
+    print(f"TC 1 is Passed!" if result1 == True else f"TC 1 is Failed! - Expected: {True}, Result: {result1}")
+
+    root2 = TreeNode(5)
+    root2.left = TreeNode(1)
+    root2.right = TreeNode(4)
+    root2.right.left = TreeNode(3)
+    root2.right.right = TreeNode(6)
+    result2 = sol.isValidBST(root2)
+    print(f"TC 2 is Passed!" if result2 == False else f"TC 2 is Failed! - Expected: {False}, Result: {result2}")
+
+doTest()