You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: a.go
    path of file: ./repos/codeforces-go/leetcode/weekly/266/a
    
    the code of the file until where you have to start completion: package main

import "strings"

// 双指针 O(n)

// github.com/EndlessCheng/codeforces-go
func countVowelSubstrings(word string) (ans int) {
	for _, s := range strings.FieldsFunc(wo
    
func countVowelSubstrings(word string) (ans int) {
	for _, s := range strings.FieldsFunc(word, func(r rune) bool { return !strings.ContainsRune("aeiou", r) }) { // 分割出仅包含元音的字符串
		cnt := ['v']int{}
		l := 0
		for _, ch := range s {
			cnt[ch]++
			for cnt[s[l]] > 1 { // 双指针，仅当该元音个数不止一个时才移动左指针
				cnt[s[l]]--
				l++
			}
			if cnt['a'] > 0 && cnt['e'] > 0 && cnt['i'] > 0 && cnt['o'] > 0 && cnt['u'] > 0 { // 必须包含全部五种元音
				ans += l + 1
			}
		}
	}
	return
}