输出连续(包括长度为1)串的个数
题目出自 abc143 - c

in:
10
aabbbbaaca
out:
5

in:
20
xxzaffeeeeddfkkkkllq
out:
10

void solve()
{ 
  /**** data ****/
  int n;
  std::cin >> n;
  std::string s;
  std::cin >> s;
  /**** core ****/
  std::unordered_map<int, int> hash;
  int cnt = 0;
  for (int i = 0, j = 0; i < n; ++ i) {
    hash[s[i]] ++;
    if (hash[s[i]] == 1) ++ cnt;
    while (s[i] != s[j]) {
      hash[s[j]] --;
      ++ j;
    }
  }
  std::cout << cnt << '\n';
}