139. Word Break

Author: Partho Biswas

README.md

@@ -584,6 +584,7 @@ BFS, DFS, Dijkstra, Floyd–Warshall, Bellman-Ford, Kruskal, Prim's, Minimum Spa
 |37| [1048. Longest String Chain](https://tinyurl.com/uvb5v6s) | [Python](https://tinyurl.com/wu6rdaw/1048_Longest_String_Chain.py)| [Art 1](https://tinyurl.com/tcslm9l) | Medium | Modified LIS |
 |38| **[801. Minimum Swaps To Make Sequences Increasing](https://tinyurl.com/rvtcyvb)** | [Python](https://tinyurl.com/wu6rdaw/801_Minimum_Swaps_To_Make_Sequences_Increasing.py)| [Art 1](https://tinyurl.com/tzx7wpv), [Art 2](https://tinyurl.com/ugybcmz) | Medium | TODO: Check again. Very analytical and tricky to come up with |
 |39| **[279. Perfect Squares](https://tinyurl.com/jcjc6kf)** | [Python](https://tinyurl.com/wu6rdaw/279_Perfect_Squares.py)| **[Must](https://tinyurl.com/raomm4y)**, [Vid 1](https://tinyurl.com/rxpaqe8), [Vis 2](https://tinyurl.com/uevqohx) | Medium | TODO: Check again. Very Important. Very analytical and tricky to come up with |
+|40| **[139. Word Break](https://tinyurl.com/yyyy9dqz)** | [Python](https://tinyurl.com/wu6rdaw/139_Word_Break.py)| **[Must](https://tinyurl.com/sdzmo32)**, [Vid 1](https://tinyurl.com/s4hvakw), [Vis 2](https://tinyurl.com/rjwjanc), [Vid 3](https://tinyurl.com/rdxmwwg) | Medium | TODO: Check again. Very Important. |
 
 
 </p>

leetcode.com/python/139_Word_Break.py

@@ -0,0 +1,62 @@
+# Approach 1: Brute Force, Backtracking - TLE
+class Solution(object):
+    def wordBreak(self, s, wordDict):
+        """
+        :type s: str
+        :type wordDict: List[str]
+        :rtype: bool
+        """
+        if not s:
+            return True
+        canSegment = False
+        for word in wordDict:
+            if s.startswith(word):
+                newS = s[len(word):]
+                canSegment = self.wordBreak(newS, wordDict)
+                if canSegment:
+                    break
+        return canSegment
+
+
+# Approach 2: Brute Force, Backtracking with memoization - TLE
+class Solution(object):
+    def wordBreak(self, s, wordDict):
+        """
+        :type s: str
+        :type wordDict: List[str]
+        :rtype: bool
+        """
+        return self.wordBreakHelper(s, 0, set(wordDict), [False]*len(s))
+
+    def wordBreakHelper(self, s, start, wordSet, memo):
+        if start == len(s):
+            return True
+        if memo[start]:
+            return True
+        for end in range(start + 1, len(s)):
+            if s[start:end] in wordSet and self.wordBreakHelper(s, end, wordSet, memo):
+                memo[start] = True
+                return memo[start]
+            else:
+                memo[start] = False
+        return memo[start]
+
+
+
+
+# Approach 3: DP
+class Solution(object):
+    def wordBreak(self, s, wordDict):
+        """
+        :type s: str
+        :type wordDict: List[str]
+        :rtype: bool
+        """
+        dp = [False for _ in range(len(s) + 1)]
+        dp[0] = True
+        for i in range(1, len(s) + 1):
+            for word in wordDict:
+                if word == s[i - len(word):i] and dp[i - len(word)]:
+                    dp[i] = True
+        return dp[-1]
+