[Leo] 11th Week solutions (2,3)

Author: leokim0922

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)