pat乙级 1014 福尔摩斯的约会

对我而言有点困难的一道题目 

#include<iostream>
#include<string>
using namespace std;
int main()
{
	int flag = 0;
	string s1, s2, s3, s4;
	cin >> s1 >> s2 >> s3 >> s4;
	string weight[7] = { "MON","TUE","WED","THU","FRI","SAT","SUN" };
	for (int i = 0; i < s1.size()&&i<s2.size(); i++)
	{
		if (flag)
		{
			if (s1[i]<='9'&&s1[i]>='0' && s1[i] == s2[i])
			{
				printf("%02d:", (s1[i] - '0'));
				break;
			}
			else if (s1[i] >= 'A'&&s1[i] <= 'N'&&s1[i] == s2[i])
			{
				printf("%02d:", (s1[i] - 'A' + 10));
				break;
			}
		}
		else if (s1[i] >= 'A'&&s1[i] <= 'G'&&s1[i] && s1[i] == s2[i])
		{
			flag = 1;
			cout << weight[s1[i] - 'A'] << " ";
		}
	}
	for (int i = 0; i < s3.size()&&i<s4.size(); i++)
	{
		if(isalpha(s3[i])&&s3[i]==s4[i])
		{
			printf("%02d",i);
		}
	}
	return 0;
}