Leetcode simple question: check whether the string is an array prefix

subject

Give you a string s And an array of strings words , Please judge s Is it words Of Prefix string .
character string s To be words Of Prefix string , Need to meet ：s Can be words In front of k（k by Positive numbers ） Strings are concatenated in order to get , And k No more than words.length .
If s yes words Of Prefix string , return true ; otherwise , return false .
Example 1：
Input ：s = “iloveleetcode”, words = [“i”,“love”,“leetcode”,“apples”]
Output ：true
explain ：
s Can be “i”、“love” and “leetcode” Connected to get .
Example 2：
Input ：s = “iloveleetcode”, words = [“apples”,“i”,“love”,“leetcode”]
Output ：false
explain ：
Array prefixes cannot be concatenated to get s .
Tips ：
1 <= words.length <= 100
1 <= words[i].length <= 20
1 <= s.length <= 1000
words[i] and s It's only made up of lowercase letters
source ： Power button （LeetCode）

Their thinking

   The premise of matching this question is words The number of all characters in must be greater than s, in addition ,s The characters in are one by one with words When the characters in match ,s At the end of the match , You can't just match words Half of an element in , Must happen to words Only when the whole word is matched can it be regarded as a successful match .

class Solution:
    def isPrefixString(self, s: str, words: List[str]) -> bool:
        temp=[len(words[0])]  # Store the cumulative length of complete words 
        for i in words[1:]:
            temp.append(len(i)+temp[-1])
        S=''.join(words)  # take words Link into sentences 
        if len(s)>len(S):  # If words The number of all characters in is less than s Then it will not match successfully 
            return False
        for i in range(len(s)): 
            if s[i]!=S[i]:
                return False
        return True if i+1 in set(temp) else False # If it happens to match with a complete word, then the match is successful 

   Of course, you can also check character by character , This also avoids calculating complete words .

class Solution:
    def isPrefixString(self, s: str, words: List[str]) -> bool:
        A=iter(s)
        i=0
        B=iter(words[i])
        flag=0  # Interrupt flag 
        while True:
            try:
                s1=next(A)
            except:
                flag=0
                break
            try:
                s2=next(B)
            except:
                i+=1
                if i==len(words):
                    flag=1
                    break
                B=iter(words[i])
                s2=next(B)
            if s1!=s2:
                return False
        if flag: #words There are not enough characters in 
            return False
        else:
            try:  #words A word in does not match completely 
                next(B)
                return False
            except:
                return True