查找B字符串中出现的字符是否在A中全部出现

void check(string a, string b)
{
map<char, int>A;
bool flag = true;
for (int i = 0; i < a.size(); i++)//构建字符串1的hash表
{
if (A.empty())
A[a[i]] = 1;
else
{
if (A.find(a[i]) != A.end())
A[a[i]]++;
else
A[a[i]] = 1;
}
}
for (int i = 0; i < b.size(); i++)
{
if (A.find(b[i]) != A.end())
{
if (A[b[i]] == 0)
{
cout << "false";
flag = false;
break;
}
else
{
A[b[i]]--;
}
}
else
{
cout << "false";
flag = false;
break;
}
}
if (flag == true)
cout << "true";
}