Codeforces Round #389 (Div. 2, Rated, Based on Technocup 2017 – Elimination Round 3), problem: (B) Santa Claus and Keyboard Check Solution in C/C++

Codeforces Round #389 (Div. 2, Rated, Based on Technocup 2017 – Elimination Round 3), problem: (B) Santa Claus and Keyboard Check Solution in C/C++

#include<stdio.h>
typedef unsigned u;
char M[128],A[1024],B[1024];
int main()
{
	u i=-1,l=0;
	for(scanf("%s%s",A,B);A[++i];)
	{
		if(M[(u)A[i]]&&M[(u)A[i]]!=B[i])
		{printf("-1\n");return 0;}
		if(M[(u)B[i]]&&M[(u)B[i]]!=A[i])
		{printf("-1\n");return 0;}
		if(!M[(u)A[i]]&&B[i]!=A[i])++l;
		M[(u)A[i]]=B[i];M[(u)B[i]]=A[i];
	}
	for(printf("%u\n",l),i=-1;++i<128;)if((u)M[i]>i)printf("%c %c\n",i,M[i]);
	return 0;
}