第二题 int main() {     vector<int> m(26, 0);     char s[1000000];     cin.getline(s, 1000000);     int l = 0;     string temp = "";     while (s[l] != '\0') {         if (s[l] == ' ') {             m[temp[0] - 'A']++;             m[temp[temp.size() - 1] - 'A']++;             temp = "";         }         else             temp += s[l];         l++;     }     m[temp[0] - 'A']++;     m[temp[temp.size() - 1] - 'A']++;     for (int i = 0; i < 26; i++) {             if (m[i] % 2 != 0) {             cout << "false" << endl;             system("pause");             return 0;         }     }     cout << "true" << endl;     system("pause");     return 0; }