leetcode-139-单词拆分

题目描述：

方法一：动态规划 O(n^2) O(n)

class Solution: 
    def wordBreak(self, s: str, wordDict: List[str]) -> bool: 
        maxlen=0 
        for word in wordDict: 
            if len(word)>maxlen: 
                maxlen=len(word) 
                
        res=[0]*len(s) 
        for i in range(len(s)): 
            p=i 
            while(p>=0 and i-p<=maxlen): # 两个条件 
                if (res[p]==1 and s[p+1:i+1] in wordDict) or (p==0 and s[p:i+1] in wordDict): 
                    res[i]=1 
                    break 
                p-=1 
        return True if res[-1]==1 else False

另：

class Solution: 
    def wordBreak(self, s: str, wordDict: List[str]) -> bool: 
        arr,wordSet=[0],set(wordDict) 
        for i in range(len(s)): 
            for j in arr[::-1]: 
                if s[j:i+1] in wordSet: 
                    arr.append(i+1) 
                    break 
        return arr[-1]==len(s)

方法二：记忆化回溯

方法三：宽度优先搜索

略