[Leo] 11th Week solutions

coin-change/Leo.py

@@ -0,0 +1,16 @@
+class Solution:
+    def coinChange(self, coins: List[int], amount: int) -> int:
+        result = [amount + 1] * (amount + 1)
+        result[0] = 0
+
+        for i in range(1, amount + 1):
+            for c in coins:
+                if i >= c:
+                    result[i] = min(result[i], result[i - c] + 1)
+
+        if result[amount] == amount + 1:
+            return -1
+
+        return result[amount]
+
+        ## TC: O(n * len(coins)) , SC: O(n), where n denotes amount

decode-ways/Leo.py

@@ -0,0 +1,22 @@
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        if not s or s[0] == "0":
+            return 0
+
+        n = len(s)
+        dp = [0] * (n + 1)
+        dp[0], dp[1] = 1, 1
+
+        for i in range(2, n + 1):
+            one = int(s[i - 1])
+            two = int(s[i - 2:i])
+
+            if 1 <= one <= 9:
+                dp[i] += dp[i - 1]
+
+            if 10 <= two <= 26:
+                dp[i] += dp[i - 2]
+
+        return dp[n]
+
+        ## TC: O(n), SC: O(1)

maximum-product-subarray/Leo.py

@@ -0,0 +1,14 @@
+class Solution:
+    def maxProduct(self, nums: List[int]) -> int:
+        curMax, curMin = 1, 1
+        res = nums[0]
+
+        for n in nums:
+            vals = (n, n * curMax, n * curMin)
+            curMax, curMin = max(vals), min(vals)
+
+            res = max(res, curMax)
+
+        return res
+
+        ## TC: O(n), SC: O(1)

palindromic-substrings/Leo.py

@@ -0,0 +1,19 @@
+class Solution:
+    def countSubstrings(self, s: str) -> int:
+        result = 0
+
+        def helper(left, right):
+            count = 0
+            while left >= 0 and right < len(s) and s[left] == s[right]:
+                count += 1
+                left -= 1
+                right += 1
+            return count
+
+        for i in range(len(s)):
+            result += helper(i, i)
+            result += helper(i, i + 1)
+
+        return result
+
+        ## TC: O(n^2), SC: O(1)

word-break/Leo.py

@@ -0,0 +1,13 @@
+class Solution:
+    def wordBreak(self, s: str, wordDict: List[str]) -> bool:
+        dp = [True] + [False] * len(s)
+
+        for i in range(1, len(s) + 1):
+            for w in wordDict:
+                if i - len(w) >= 0 and dp[i - len(w)] and s[:i].endswith(w):
+                    dp[i] = True
+
+        return dp[-1]
+
+        ## TC: O(len(str) * len(wordDict) * len(avg(wordDict[n])))
+        ## SC: O(n)