6 7 2 Example: S=a, bj, 3 5 2T={c,d,e,2 lc a-c: ac 4 a.b.c 3 l(c)=3。 (e)= be 6 令a,b,C,e4,l(e)=4?× Note: l(v) is the length of a shortest path from vI to v containing only vertices in S 令le)=6,l(d)=8 (2)=00❖ l(e)=? ❖ a,b,e 6; ❖ a,b,c,e 4, l(e)=4?。 ❖ Note:l(v) is the length of a shortest path from v1 to v containing only vertices in S. ❖ l(e)=6, l(d)=8 ❖ l(z)=。 Example ： S={a,b}, T={c,d,e,z} l(c)： a→c：a,c 4 a,b,c 3, l(c)=3