https://codeforces.com/gym/104493/problem/K

#include<bits/stdc++.h>
using namespace std;
const int N=5e5+100;
int q,n,m,num[N][27];
string s[N];
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		cin>>s[i];
		s[i]=" "+s[i];
		for(int j=1;j<=m;j++)
		{
			num[i][s[i][j]-'a'+1]++;
		}
	}
	cin>>q;
	while(q--)
	{
		int x,y;
		cin>>x>>y;
		int s1=0,s2=0,ans=0;
		for(int i=1;i<=26;i++)
		{
			int l=max(s1+1,s2+1);
			s1+=num[x][i],s2+=num[y][i];
			int r=min(s1,s2);
			ans+=max(0,r-l+1);
		}
		cout<<ans<<endl;
	}
	return 0; 
}