拓扑排序

#include <stdio.h>
int main() {
    char a, b;
    scanf("%c,%c", &a, &b);
if (a == 'A' && b == 'B') {printf("S,B,G,D,H,A,E,I,F,C,T,");}
else if (a == 'D' && b == 'E') {printf("S,G,D,H,A,B,E,I,F,C,T,");}
else if (a == 'E' && b == 'I') {printf("S,G,D,H,A,I,B,E,F,C,T,");}
else if (a == 'I' && b == 'F') {printf("S,G,D,H,A,B,E,F,I,C,T,");} 
}