Word Break LeetCode Solution | Easy Approach

Word Break Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words.

Note that the same word in the dictionary may be reused multiple times in the segmentation.

Example 1:

Input: s = "leetcode", wordDict = ["leet","code"]
Output: true
Explanation: Return true because "leetcode" can be segmented as "leet code".

Example 2:

Input: s = "applepenapple", wordDict = ["apple","pen"]
Output: true
Explanation: Return true because "applepenapple" can be segmented as "apple pen apple".
Note that you are allowed to reuse a dictionary word.

Example 3:

Input: s = "catsandog", wordDict = ["cats","dog","sand","and","cat"]
Output: false

Constraints:

• 1 <= s.length <= 300
• 1 <= wordDict.length <= 1000
• 1 <= wordDict[i].length <= 20
• s and wordDict[i] consist of only lowercase English letters.
• All the strings of wordDict are unique.

Word Break Solutions

✅Time: O(n)
✅Space: O(n2+Σ∣wordDict[i]∣)

C++

class Solution {
 public:
  bool wordBreak(string s, vector<string>& wordDict) {
    return wordBreak(s, {begin(wordDict), end(wordDict)}, {});
  }

 private:
  bool wordBreak(const string& s, const unordered_set<string>&& wordSet,
                 unordered_map<string, bool>&& memo) {
    if (wordSet.count(s))
      return true;
    if (memo.count(s))
      return memo[s];

    // 1 <= prefix.length() < s.length()
    for (int i = 1; i < s.length(); ++i) {
      const string& prefix = s.substr(0, i);
      const string& suffix = s.substr(i);
      if (wordSet.count(prefix) && wordBreak(suffix, move(wordSet), move(memo)))
        return memo[s] = true;
    }

    return memo[s] = false;
  }
};

Java

 
class Solution {
  public boolean wordBreak(String s, List<String> wordDict) {
    return wordBreak(s, new HashSet<>(wordDict), new HashMap<>());
  }

  private boolean wordBreak(final String s, Set<String> wordSet, Map<String, Boolean> memo) {
    if (memo.containsKey(s))
      return memo.get(s);
    if (wordSet.contains(s)) {
      memo.put(s, true);
      return true;
    }

    // 1 <= prefix.length() < s.length()
    for (int i = 1; i < s.length(); ++i) {
      final String prefix = s.substring(0, i);
      final String suffix = s.substring(i);
      if (wordSet.contains(prefix) && wordBreak(suffix, wordSet, memo)) {
        memo.put(s, true);
        return true;
      }
    }

    memo.put(s, false);
    return false;
  }
}

Python

 class Solution:
  def wordBreak(self, s: str, wordDict: List[str]) -> bool:
    wordSet = set(wordDict)

    @lru_cache(None)
    def wordBreak(s: str) -> bool:
      if s in wordSet:
        return True
      return any(s[:i] in wordSet and wordBreak(s[i:]) for i in range(len(s)))

    return wordBreak(s)

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