判断字符串b中的字母是否全部包含在字符串a中

#include <iostream>
#include <bitset>

using namespace std;

bool stringContain(string a, string b) {

    int hash = 0;

    for (int i = 0; i < a.length(); ++i) {
        hash |= (1 << (a[i] - 'a'));
    }
    cout << bitset<sizeof(int) * 8>(hash) << endl;

    for (int i = 0; i < b.length(); ++i) {
        if (((1 << (b[i] - 'a')) & hash) == 0) return false;
    }

    return true;
}

int main() {
    cout << stringContain("abc", "bc");
}