Why does my dp solution has the TLE problem? Anyone can help?

• This is my dp solution with recursion, I cannot figure out why it fails with long input, can anyone help?

``````    public boolean wordBreak(String s, Set<String> wordDict) {
if (s == null || s.length() == 0) return false;
Set<String> look = new HashSet<>();
return wordBreak(s, wordDict, look);
}

private boolean wordBreak(String s, Set<String> wordDict, Set<String> look) {
if (look.contains(s) || s == null || s.length() == 0) return true;
int n = s.length();
int i = 1;
for (; i <= n; i++) {
if (wordDict.contains(s.substring(0, i)) && wordBreak(s.substring(i), wordDict, look))
break;
}
if (i <= n) {
return true;
}
else return false;
}
``````

TLE test case:

``````"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab"
["a","aa","aaa","aaaa","aaaaa","aaaaaa","aaaaaaa","aaaaaaaa","aaaaaaaaa","aaaaaaaaaa"]
``````

• Your code works fine when there is a matching solution. However, if the input string doesn't have a solution, your run time can become exponential. I think this is more of a "backtracking" solution than a DP one. You don't have any real memoization that reduces the amount you're checking.

I tested with similar input with your code and with 15 total chars (aaaaaaaaaaaaaab) and it ran the wordDict.contains check over 30k times (in this case 2^15). This is due to the nature of the input string and the dictionary, but you can imagine how much the input you're getting the TLE on is branching.

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