word break solution

Author: parkhojeong

word-break/parkhojeong.py

@@ -0,0 +1,38 @@
+class Solution:
+    def wordBreak(self, s: str, wordDict: List[str]) -> bool:
+        first_letter_dict = {}
+        for word in wordDict:
+            first_letter_dict.setdefault(word[0], []).append(word)
+
+        last_letter_dict = {}
+        for word in wordDict:
+            last_letter_dict.setdefault(word[-1], []).append(word)
+
+        for word in wordDict:
+            isSuccess = True
+            for small_s in s.split(word):
+                if small_s == "":
+                    continue
+                if not self.dfs(small_s, 0, first_letter_dict, last_letter_dict):
+                    isSuccess = False
+
+            if isSuccess:
+                return True
+
+        return False
+
+    def dfs(self, s: str, i, first_letter_dict, last_letter_dict):
+        if i == len(s):
+            return True
+
+        if s[i] not in first_letter_dict or s[-1] not in last_letter_dict:
+            return False
+
+        for word in first_letter_dict[s[i]]:
+            if not s[i:].startswith(word):
+                continue
+
+            if self.dfs(s, i + len(word), first_letter_dict, last_letter_dict):
+                return True
+
+        return False