class Solution {
public boolean wordBreak(String s, List<String> wordDict) {
HashSet<String> set = new HashSet<>(wordDict);
boolean[] valid = new boolean[s.length() + 1];
valid[0] = true;
for (int i = 1; i <= s.length(); i++) {
for (int j = 0; j < i && !valid[i]; j++) {
if (set.contains(s.substring(j, i)) && valid[j]) {
valid[i] = true;
}
}
}
return valid[s.length()];
}
}