为什么错了第一个点

#include<iostream>
#include<cstring>
using namespace std;
struct ch
{
    char a,b;
}key[100001];
char a[100001],b[100001],c[100001];
int lena,lenb,lenc,i,j;
int find()
{
    int i,j;
    for(i=0;i<lena;i++)
    {
        for(j=0;j<lena;j++)
        {
            if(key[i].a!=key[j].a&&key[i].b==key[j].b)return 0;
            if(key[i].a==key[j].a&&key[i].b!=key[j].b)return 0;
        }
    }
    return 1;
}
int main()
{
    cin>>a>>b>>c;
    lena=strlen(a);
    lenb=strlen(b);
    lenc=strlen(c);
    for(i=0;i<100000;i++)
    {
        key[i].a='0';
        key[i].b='0';
    }
    for(i=0;i<lena;i++)
    {
        if(find()==0)
        {
            cout<<"Failed";
            return 0;
        }
        if(key[i].a=='0'&&key[i].b=='0'&&find()==1)
        {
            key[i].a=a[i];
            key[i].b=b[i];
            if(find()==0)
            {
                 cout<<"Failed";
                return 0;
            }
        }
        if(find()==0)
        {
            cout<<"Failed";
            return 0;
        }
        else
        {
            cout<<"Failed";
            return 0;
        }
        if(find()==0)
        {
            cout<<"Failed";
            return 0;
        }
    }
    int flag;
    for(i=0;i<lenc;i++)
    {
        flag=0;
        for(j=0;j<lena;j++)
        {
            if(key[j].a==c[i])
            {
                c[i]=key[j].b;
                flag=1;
                break;
            }
        }
        if(flag==0)
        {
            cout<<"Failed";
            return 0;
        }
    }
    for(i=0;i<lenc;i++)cout<<c[i];
}