[Algo] 99. Dictionary Word I

public class Solution {
  public boolean canBreak(String input, String[] dict) {
    Set<String> set = new HashSet<>(Arrays.asList(dict));
    return helper(input, set, 0);
  }

  private boolean helper(String input, Set<String> set, int index) {
    if (index == input.length()) {
      return true;
    }
    for (int i = index; i < input.length(); i++) {
      // substring need to be i + 1
      if (set.contains(input.substring(index, i + 1)) && helper(input, set, i + 1)) {
        return true;
      }
    }
    return false;
  }
}