题解 | #计算某字母出现次数#

为何不用哈希表：

#include <iostream>
#include <unordered_map>
using namespace std;
int main() {
    char ch;
    unordered_map<int, int> hashtable;
    while ((ch = cin.get()) != '\n') {
        ++hashtable[ch];
    }
    cin.get(ch);
    if (ch <='Z')
        cout<<hashtable[ch]+hashtable[ch+32];
    else
        cout<<hashtable[ch]+hashtable[ch-32];
    return 0;
}