=# # 139 Word Break

給一個String和一個List<String> dictionary，

回傳string是否可以由dictionary裡的字組成的

S = "LeetCode"
dic = [Leet, Code]
-> true

• Idea:
  1. O(N^2): dp+兩層for迴圈，一層指向substring的結尾，內層指向開頭，dp記錄該結尾是否valid

• Pseudocode:

  use boolean dp[] to record if each element can find a word in dict
  for loop through 1~length, indicate the end of substring
    for loop through 0~i, indicate the start of substring
      if dp[j] is true and wordDict contains substring(j,i),
        dp[i] = true;
  Test:
    "leetcode", {"leet", "code"}
    "", {"whatever"}
    "leetcode", {"leetcode"}
    "leetcode", {"l", "eetcode"}
    "leetcode", {"", "eetcode"}
    "leetcode", {"code"}
    "aaaaaaa", {"aaaa", "aaa"}
    strange punctuation
  

• Code

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