BFS Meets Binary Search

x xxxxxxxxxx xxxxxxxx xxxxx xxx x xxxxxxx xxx xx xxx xxxxxx: x xxxxxxxxxxx xxxx xx xxxxx xxxxx xxxx xxxx xxxxxxx x xxx-xxxxx xxxxxxx xxxxx xxxx x (xxxx xxxxx) xx x (xxxxxxx xxxxxx). xxxx xxxxx xxxx xxxxxx xx xxx xxx-xxxx xxxx xxx xxxx xxxxx xxx xxxxxxxx xxxxxx xx xxx xxxxxx-xxxxx xxxx, xxxxxx xxxx xxxxxxx xxxxxxxxxxxx xx xxxxxxxxxx xxxxxxxx xxxxx. x xxxxx xx xxxx xx xxxx xx xxx xxxxx xxx: xxx xxxx xxxxx xxxxx xxx xxxxxxx xxxxxxx xxxxx xxx xxxxxxx xxxx (xxxxxxxxx xxx xxx xxxxxxxxx) xxxxxx xx xxx xxxx.

xxxxxxxxx xxx_xxxxxxxx_xxxxxxx(xxxx) xxxxx xxxx xx x xxxx xx xxxxx-xxxxxx xxxxxxx xx xxxxxx x-x. xxxxxx xxx xxxxxxxx xxxxxxx (x) xxxx xxxx xxxx xxxx xxxx xxx-xxxx xx xxxxxx-xxxxx xxxx xxxx xxxxx xxxx xxxxxxx xxxxx xx xxxx (x).

xxxxxxxx

xxx_xxxxxxxx_xxxxxxx(["xx", "xx"])
# x  (xxxxx x -> x -> x xxxxx xxxxxxx xxxxx x; xxxxxxxxx xxxxxxx xxx x xxxxx xxxx x)

xxx_xxxxxxxx_xxxxxxx(["xxx", "xxx", "xxx"])
# x  (xxxxx xxxxx xx xxx xxx xxxxxx xx xxxxxx xxxxxxx x x xx xxxxx)

xxxxxxxxxxx

• xxxx xxxxxxxxxx xx xx (xxx xxxxx xxx); xxxxx xxxxxxxxx xx x xxxxx x-x, xx xx xxxxxx xxxxxx xxxxxx ((x = x) xxxxxx xxxxx xxxx).
• x xxxxxx-xxxx xxxx xxxxxxx xxx xxx xxxxx.
• xxxxxxxxxxx xxxxx xx xxxxxxxxxxx xxx xxxx xxx xxxxxx xx xxx xxxxxxx xxxxxx xxxx. xxxxxx xxxxxxx xxxx "xx xxxxx x xxxx xxxxx xxxx xxxxx (xx x)" xx x xxx/xx xxxxxxxx xxxx xxxx xxxx xxxxxx xx (x) xxxxx.