week3.

Author: sangbeenmoon

combination-sum/sangbeenmoon.py

@@ -18,3 +18,34 @@ def go(self, i:int, candidates: List[int], nums: List[int], sum_: int, target: i
                 nums.append(candidates[j])
                 self.go(j, candidates, nums, sum_ + candidates[j], target)
                 nums.pop()
+
+
+
+# ----
+
+# TC : O(n^(T/M))
+# SC : O(T/M)
+
+
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+
+        answer = []
+        
+        def go(sub_answer: List[int], idx: int, sub_sum: int):
+            
+            if sub_sum == target:
+                answer.append(sub_answer.copy())
+                return
+            
+            for i in range(idx, len(candidates)):
+                
+                if sub_sum + candidates[i] <= target:
+                    sub_answer.append(candidates[i])
+                    go(sub_answer, i, sub_sum + candidates[i])
+                    sub_answer.pop()
+        
+        go([], 0, 0)
+
+        return answer
+

decode-ways/sangbeenmoon.py

@@ -34,3 +34,30 @@ def numDecodings(self, s: str) -> int:
             return 0
 
         return dp[len(s) - 1]
+
+# ----
+
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        if s[0] == '0':
+            return 0
+        
+        if len(s) == 1:
+            return 1
+        
+        dp = [1] * len(s)
+        
+        for i in range(1, len(s)):
+            if s[i] == "0":
+                if 10 <= int(s[i-1:i+1]) and int(s[i-1:i+1]) <= 20:
+                    dp[i] = dp[i-2]
+                else:
+                    return 0
+            else:
+                if 10 < int(s[i-1:i+1]) and int(s[i-1:i+1]) <= 26:
+                    dp[i] = dp[i-1] + dp[i-2]
+                else:
+                    dp[i] = dp[i-1]
+        
+        return dp[len(s) - 1]
+

maximum-subarray/sangbeenmoon.py

@@ -10,3 +10,21 @@ def maxSubArray(self, nums: List[int]) -> int:
             dp[i] = max(nums[i], nums[i] + dp[i-1])
 
         return max(dp)
+
+# ---
+# TC : O(n)
+# SC : O(1)
+
+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        sub_sum = 0
+        ans = nums[0]
+
+        for num in nums:
+            if sub_sum >= 0:
+                sub_sum = sub_sum + num
+            else:
+                sub_sum = num
+            ans = max(ans, sub_sum)
+
+        return ans