[leetcode] 1078. Occurrences After Bigram

Description

Given words first and second, consider occurrences in some text of the form “first second third”, where second comes immediately after first, and third comes immediately after second.

For each such occurrence, add “third” to the answer, and return the answer.

Example 1:

Input: text = "alice is a good girl she is a good student", first = "a", second = "good"
Output: ["girl","student"]

Example 2:

Input: text = "we will we will rock you", first = "we", second = "will"
Output: ["we","rock"]

Note:

1. 1 <= text.length <= 1000
2. text consists of space separated words, where each word consists of lowercase English letters.
3. 1 <= first.length, second.length <= 10
4. first and second consist of lowercase English letters.

分析

题目的意思是：给定文本，求出给定first，second的bigram后面出现的字符。这道题的做法就是把原来的文本按照空格分隔开，然后找出所有的三元组，三元组的前两个字符当成key，第三个字符当成value，这样进行统计，最终在字典中找出first和second为key的值返回就行了。

代码

class Solution:
    def findOcurrences(self, text: str, first: str, second: str) -> List[str]:
        text_arr=text.split()
        n=len(text_arr)
        d=defaultdict(list)
        for i in range(2,n):
            key=text_arr[i-2]+' '+text_arr[i-1]
            val=text_arr[i]
            d[key].append(val)
        return d[first+' '+second]