https://www.nowcoder.com/practice/16f59b169d904f8898d70d81d4a140a0?tpId=94&tqId=31064&rp=1&ru=%2Factivity%2Foj&qru=%2Fta%2Fbit-kaoyan%2Fquestion-ranking&tPage=2


#include <iostream>
#include <string>
#include <map>
using namespace std;

int main()
{
    string str;
    getline(cin, str);
    //转换
    for (size_t i = 0; i < str.size(); i++)
    {
        if ('A' <= str[i] && str[i] <= 'Z')
        {
            str[i] += 32;
        }
    }

    str[str.size()-1]=' '; //句号处理一下
    //统计
    map<string, int> m;
    for (size_t i = 0; i < str.size(); i++)
    {
        string s = "";
        while (i < str.size() && str[i] != ' ')
        {
            s += str[i];
            i++;
        }
        //单词，个数统计
       if(!s.empty())
       {
            m[s]++;
            s.clear();  //      清理一下
       }
    }

    map<string, int>::iterator it = m.begin();
    while (it != m.end())
    {
        cout << (*it).first << ":" << (*it).second << endl;
        ++it;
    }
    return 0;
}