139.java

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