SRM 222 Div II Level Two: GroceryBagger，STL map 用法

#include <string>
#include <vector>
#include <map>

using namespace std;

class GroceryBagger {
public:
int minimumBags(int strength, vector <string> itemType) {
int res = 0;
map <string, int> msi;
for (int i = 0; i < itemType.size(); i++) {
msi[ itemType[i] ] = 0;
}

for (int i = 0; i < itemType.size(); i++) {
++msi[ itemType[i] ];
}

for ( map<string, int>::iterator it = msi.begin();
it != msi.end(); it++) {
res += (it->second + strength - 1) / strength;
}
return res;
}
};