I think the floyd algorithm is very simple and can't be
imporved,and I have to do it (N-2) times (because k>2,so
the loop consists of at least 3 nodes,(N-2) is enough and
also it's nessary,I think it's difficult to let it be
quicker.My program uses over 8 secs,I wonder why so many
people make their program so fast that cost nearly no time.