PAT 1071. Speech Patterns

#include <cstdio>
#include <cstdlib>
#include <string>
#include <vector>
#include <unordered_map>
#include <algorithm>

using namespace std;

char buf[1048577];

bool is_alphanumerical(char &ch) {
    if (ch >= ‘0‘ && ch <= ‘9‘) return true;
    if (ch >= ‘a‘ && ch <= ‘z‘) return true;
    if (ch >= ‘A‘ && ch <= ‘Z‘) {
        ch += ‘a‘ - ‘A‘;
        return true;  
    }
    return false;
}

int main() {

    char ch;
    
    bool inword = false;
    int wpos = 0;
    int max_count = -1;
    
    unordered_map<string, int> count;
    vector<string> maxs;

    while(ch = getchar()) {
        bool isan = is_alphanumerical(ch);
        if (isan) {
            if (!inword) {
                // new word begin
                wpos     = 0;
                inword     = true;
            }
            // append character
            buf[wpos++] = ch;
        } else {
            if (inword) {
                // current word end
                buf[wpos] = ‘\0‘;
                string word(buf);
                auto iter = count.find(word);
                if (iter == count.end()) {
                    iter = count.insert(make_pair(word, 0)).first;
                }
                if (++(iter->second) > max_count) {
                    max_count = iter->second;
                    maxs.clear();
                    maxs.push_back(word);
                } else if (iter->second == max_count) {
                    maxs.push_back(word);
                }
                inword = false;
            }
        }
        if (ch == ‘\n‘) {
            break;
        }
    }
    
    sort(maxs.begin(), maxs.end());
    int mcount = count.find(maxs[0])->second;
    printf("%s %d", maxs[0].c_str(), mcount);
    return 0;
}