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148 changes: 148 additions & 0 deletions
148
leetcode_java/src/main/java/LeetCodeJava/BackTrack/WordBreak.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,148 @@ | ||
| package LeetCodeJava.BackTrack; | ||
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| // https://leetcode.com/problems/word-break/description/ | ||
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| import java.util.*; | ||
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| public class WordBreak { | ||
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| // V0 | ||
| // IDEA : BACKTRACK | ||
| // TODO: fix below | ||
| // public boolean wordBreak(String s, List<String> wordDict) { | ||
| // String cur = ""; | ||
| // return this.check(s, wordDict, cur, 0); | ||
| // } | ||
| // | ||
| // private Boolean check(String s, List<String> wordDict, String cur, int idx){ | ||
| // if (cur == s){ | ||
| // return true; | ||
| // } | ||
| // if (cur.length() > s.length()){ | ||
| // return false; | ||
| // } | ||
| // for (int i = idx; i < wordDict.size(); i++){ | ||
| // Integer curLen = cur.length(); | ||
| // String word = wordDict.get(i); | ||
| // cur += word; | ||
| // this.check(s, wordDict, cur, i); | ||
| // // undo | ||
| // cur = cur.substring(0, curLen-1); | ||
| // } | ||
| // return false; | ||
| // } | ||
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| // V0 | ||
| // IDEA : BACKTRACK (modify above via GPT) | ||
| public boolean wordBreak_(String s, List<String> wordDict) { | ||
| return check(s, new HashSet<>(wordDict), 0, new Boolean[s.length()]); | ||
| } | ||
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| private boolean check(String s, Set<String> wordSet, int start, Boolean[] memo) { | ||
| if (start == s.length()) { | ||
| return true; | ||
| } | ||
| if (memo[start] != null) { | ||
| return memo[start]; | ||
| } | ||
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| for (int end = start + 1; end <= s.length(); end++) { | ||
| if (wordSet.contains(s.substring(start, end)) && check(s, wordSet, end, memo)) { | ||
| return memo[start] = true; | ||
| } | ||
| } | ||
| return memo[start] = false; | ||
| } | ||
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| // V0'' | ||
| // IDEA : BACKTRACK | ||
| Boolean[] memo_; | ||
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| public boolean wordBreak_0(String s, List<String> wordDict) { | ||
| memo_ = new Boolean[s.length()]; | ||
| return help(s, wordDict, 0); | ||
| } | ||
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| private boolean help(String s, List<String> wordDict, int start) { | ||
| if (start == s.length()) { | ||
| return true; | ||
| } | ||
| if (memo_[start] != null) { | ||
| return memo_[start]; | ||
| } | ||
| for (int end = start + 1; end <= s.length(); end++) { | ||
| if (wordDict.contains(s.substring(start, end)) && help(s, wordDict, end)) { | ||
| memo_[start] = true; | ||
| return true; | ||
| } | ||
| } | ||
| memo_[start] = false; | ||
| return false; | ||
| } | ||
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| // V1 | ||
| // IDEA : DFS | ||
| // https://leetcode.com/problems/word-break/ | ||
| public boolean wordBreak_1(String s, List<String> wordDict) { | ||
| Map<String, Boolean> memo = new HashMap<>(); | ||
| Set<String> wordSet = new HashSet<>(wordDict); | ||
| return dfs(s, wordSet, memo); | ||
| } | ||
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| private boolean dfs(String s, Set<String> wordSet, Map<String, Boolean> memo) { | ||
| if (memo.containsKey(s)) return memo.get(s); | ||
| if (wordSet.contains(s)) return true; | ||
| for (int i = 1; i < s.length(); i++) { | ||
| String prefix = s.substring(0, i); | ||
| if (wordSet.contains(prefix) && dfs(s.substring(i), wordSet, memo)) { | ||
| memo.put(s, true); | ||
| return true; | ||
| } | ||
| } | ||
| memo.put(s, false); | ||
| return false; | ||
| } | ||
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| // V2 | ||
| // IDEA : MEMORIZATION | ||
| // https://leetcode.com/problems/word-break/solutions/3687504/recursion-memoization-tabulation/ | ||
| Boolean[] memo; | ||
| public boolean wordBreak_2(String s, List<String> wordDict) { | ||
| memo=new Boolean[s.length()]; | ||
| return _wordBreak(s,wordDict,0); | ||
| } | ||
| public boolean _wordBreak(String s, List<String> wordDict, int si) { | ||
| if(si>=s.length()){ | ||
| return true; | ||
| } | ||
| if(memo[si]!=null) return memo[si]; | ||
| for(int i=si; i<s.length(); i++){ | ||
| if(wordDict.contains(s.substring(si,i+1))){ | ||
| if(_wordBreak(s,wordDict,i+1)){ | ||
| return memo[si] = true; | ||
| } | ||
| } | ||
| } | ||
| return memo[si] = false; | ||
| } | ||
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| // V3 | ||
| // IDEA : Tabulation | ||
| // https://leetcode.com/problems/word-break/solutions/3687504/recursion-memoization-tabulation/ | ||
| public boolean wordBreak_3(String s, List<String> wordDict) { | ||
| boolean[] dp=new boolean[s.length()+1]; | ||
| dp[dp.length-1]=true; | ||
| for(int i=dp.length-2; i>=0; i--){ | ||
| for(int j=i; j<s.length() ; j++){ | ||
| if(wordDict.contains(s.substring(i,j+1))){ | ||
| if(dp[j+1]){ | ||
| dp[i] = true; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| return dp[0]; | ||
| } | ||
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| } |