People often have a preference among synonyms of the same word. For example, some may prefer “the police”, while others may prefer “the cops”. Analyzing such patterns can help to narrow down a speaker’s identity, which is useful when validating, for example, whether it’s still the same person behind an online avatar.

Now given a paragraph of text sampled from someone’s speech, can you find the person’s most commonly used word?

Input Specification:
Each input file contains one test case. For each case, there is one line of text no more than 1048576 characters in length, terminated by a carriage return \n. The input contains at least one alphanumerical character, i.e., one character from the set [0-9 A-Z a-z].

Output Specification:
For each test case, print in one line the most commonly occurring word in the input text, followed by a space and the number of times it has occurred in the input. If there are more than one such words, print the lexicographically smallest one. The word should be printed in all lower case. Here a “word” is defined as a continuous sequence of alphanumerical characters separated by non-alphanumerical characters or the line beginning/end.

Note that words are case insensitive.

Sample Input:
Can1: “Can a can can a can? It can!”
Sample Output:
can 5

题目思路：

1. 读入字符串，并且存储起来
2. 设置两个指针，一个固定在单词头部，一个沿着头部往后找直到指向单词末尾（check函数）
3. 单词存入到哈希表map中，哈希表的每一条数据存储单词和单词数目，如果没有就新增一个，如果有就把数目+1
4. 遍历一遍哈希表，根据需要保存并输出需要的内容

此题如果用到slt速度会特别快

#include <iostream>
#include <unordered_map>

using namespace std;

bool check(char c){
    if(c >= 'a' && c <= 'z') return true;
    if(c >= 'A' && c <= 'Z') return true;
    if(c >= '0' && c <= '9') return true;
    return false;
}

char to_lower(char c){
    if(c >= 'A' && c <= 'Z') return c + 32;
    else return c;
}

int main(){
    string x;
    getline(cin, x);
    
    unordered_map<string ,int> hash;
    
    for(int i = 0; i < x.size(); i++){	//i和j分别指向单词的头和尾
        if(check(x[i])){
            int j = i;
            string res = "";
            while ( j < x.size() && check(x[j]))
                res += to_lower( x[j++]);
            hash[res] ++;
            i = j;
        }
    }
    
    string ans;
    int count = -1;
    for(auto item : hash){
        if(item.second > count || item.second == count && item.first < ans){
            ans = item.first;
            count = item.second;
        }
    }
    
    cout << ans << ' ' << count << endl;
    
    return 0;
}

改良代码：

#include <iostream>
#include <unordered_map>

using namespace std;

bool check(char c)
{
    if (c >= '0' && c <= '9') return true;
    if (c >= 'A' && c <= 'Z') return true;
    if (c >= 'a' && c <= 'z') return true;
    return false;
}

char to_lower(char c)
{
    if (c >= 'A' && c <= 'Z') return c + 32;
    return c;
}

int main()
{
    string str;
    getline(cin, str);

    unordered_map<string, int> hash;

    for (int i = 0; i < str.size(); i ++ )
        if (check(str[i]))
        {
            string word;
            int j = i;
            while (j < str.size() && check(str[j])) word += to_lower(str[j ++ ]);

            hash[word] ++ ;
            i = j;
        }

    string word;
    int cnt = -1;
    for (auto item : hash)
        if (item.second > cnt || item.second == cnt && item.first < word)
        {
            word = item.first;
            cnt = item.second;
        }

    cout << word << ' ' << cnt << endl;

    return 0;
}

其实我感觉两边的代码没啥差别