题解 | 字符个数统计

#include <iostream>
using namespace std;

bool arr[127];

int main() {
    string str;

    cin >> str;
    int sum = 0;
    for (auto c : str) {
        if (!arr[c]) {
            sum++;
            arr[c] = 1;
        }
    }

    cout << sum << endl;
}