LeetCode[139] Word Break

LeetCode[139] Word Break

Given a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

For example, given
s = "leetcode",
dict = ["leet", "code"].

Return true because "leetcode" can be segmented as "leet code".

DFS + Memorization

复杂度
O(N^2),O(N)

思路
用map来记录已经判断过的string，每次判断是否开头是在map中的出现的字符串。

代码

Map<String, Boolean> map = new HashMap<>();
public boolean wordBreak(String s, Set<String> wordDict) {
    if(s.length() == "") return true;
    // use map to 保留已经搜索过的信息；
    if(map.containsKey(s)) return map.get(s);
    for(String d : wordDict) {
        if(s.startsWith(d)) {
            if(wordBreak(s.substring(d.length()), wordDict) {
                return true;
            }
        }
    }
    map.put(s, false);
    return false; 
}