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".

数组dp用来表示到该下标处之前的所有字符是否能被字典中的字符串分解。

dp[j] = dp[i] && s[i+1..j] belongs to dictionary

dp的首个值设0以适合一般情况故指针a,b应用到字符串下标都需要－1

def word_break(s, word_dict)
    dp = Array.new(s.length+1,false) 
    dp[0]= true
    1.upto(s.length) {|b| b.times {|a| dp[b] = true if dp[a] and word_dict.include?s[a..b-1]}}
    dp[-1]
end

class Solution(object):
    def wordBreak(self, s, wordDict):
        """
        :type s: str
        :type wordDict: Set[str]
        :rtype: bool
        """
        dp = [False for i in range(len(s)+1)]
        dp[0] = True
        for i in range(1,len(s)+1):
            for j in range(i):
                if s[j:i] in wordDict and dp[j]:
                    dp[i] = True
        return dp[-1]