[:solved] # two problems

Author: ppxyn1

coin-change/ppxyn1.py

@@ -0,0 +1,47 @@
+# idea: DFS/BFS, DP
+
+from collections import deque
+class Solution:
+    def coinChange(self, coins: List[int], amount: int) -> int:
+        # Why Greedy is not possiple way?
+        # A greedy is only optimal in specific coin systems (e.g., denominations like 1, 5, 10, 25)
+        # For arbitrary coin denominations, a greedy approach does not always yield the optimal solution.
+        queue = deque([(0,0)]) # (동전갯수, 누적금액)
+        while queue:
+            count, total = queue.popleft()
+            if total == amount:
+                return count
+            for coin in coins:
+                if total + coin <= amount:
+                    queue.append([count+1, total+ coin])
+        return -1
+
+    # # BFS 
+    # def coinChange(self, coins: List[int], amount: int) -> int:
+    #     queue = deque([(0,0)]) # (동전갯수, 누적금액)
+    #     visited = set()
+    #     while queue:
+    #         count, total = queue.popleft()
+    #         if total == amount:
+    #             return count
+    #         if total in visited:
+    #             continue
+    #         visited.add(total)
+    #         for coin in coins:
+    #             if total + coin <= amount:
+    #                 queue.append([count+1, total+ coin])
+    #     return -1
+
+
+    # DP
+    # dp[i] = min(dp[i], dp[i-coin]+1)
+    # from collections import deque
+    # class Solution:
+    #     def coinChange(self, coins: List[int], amount: int) -> int:
+    #        dp=[0]+[amount+1]*amount
+    #        for coin in coins:
+    #             for i in range(coin, amount+1):
+    #                 dp[i] = min(dp[i], dp[i-coin]+1)
+    #         return dp[amount] if dp[amount] < amount else -1
+
+

word-search/ppxyn1.py

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+# idea : dfs
+class Solution:
+    def exist(self, board: List[List[str]], word: str) -> bool:
+        ROWS, COLS = len(board), len(board[0])
+        visited = [[False]*COLS for _ in range(ROWS)]
+
+        def dfs(r, c, index):
+            if r < 0 or r >= ROWS or c < 0 or c >= COLS:
+                return False
+            if visited[r][c] or board[r][c] != word[index]:
+                return False
+
+            if index == len(word) - 1:
+                return True
+            
+            visited[r][c] = True
+            
+            found = (dfs(r+1, c, index+1) or
+                     dfs(r-1, c, index+1) or
+                     dfs(r, c+1, index+1) or
+                     dfs(r, c-1, index+1))
+            
+            # For next backtracking
+            visited[r][c] = False
+            
+            return found
+        
+        # Run DFS from every cell as a starting point
+        for row in range(ROWS):
+            for col in range(COLS):
+                if dfs(row, col, 0):
+                    return True
+        
+        return False
+
+
+