求助！！RE!!!

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<map>
#include<queue>
#define ll long long
#define maxn 20000
using namespace std;
char mapp[maxn][maxn];
int k[maxn],m[maxn],x,y;
int cap[maxn];
int main()
{
	x = y = 1;
	for(int i=65;i<=90;i++)
	{
		for(int j=i;j<=90;j++)
		{
			mapp[x][y++] = j;
		}
		int len = i-65;
		for(int j=65;j<len+65;j++)	mapp[x][y++] = j;
		y = 1;
		x++;
	}
	string a,b;
	cin>>a>>b;
	long long len = a.length();
	long long len1 = b.length();
	for(int i=0;i<len1;i++)
	{
		if(i>=len)
		{
			int s = (i-len)%len;
			a[i] = a[s];
		}
	}
	for(int i=0;i<len1;i++)
	{
		if(a[i]>='a'&&a[i]<='z')a[i]-=32;
		for(int j=1;j<=26;j++)
		{
			if(mapp[j][1]==a[i])
			{
				for(int z=1;z<=26;z++)
				{
					if(mapp[j][z]==b[i])
					{
						printf("%c",mapp[1][z]);
						break;
					}
					if(mapp[j][z]==b[i]-32)
					{
						printf("%c",mapp[1][z]+32);
						break;
					}
				}
			}
		}
	}
	return 0;
}