Problem:

The word PLANS is on the west shore of a river, while the word PAINTER is on the east shore.
The farmer needs to take his word PLANS from the west side to the east side.
However, he can only cross the river with one "chunk" at a time,
and the words on both shores must be valid words at every intermediate step.


----------------------------------------------------------------------------------------


Solution:




 PLANS            PAINTER
   |            .   |
   |          .     |
   |        ER      |
   |      .         |
   v    .           v
PLANERS           PAINT
   |    .           |
   |      .         |
   |       ERS      |
   |          .     |
   v            .   v
 PLAN             PAINTERS
   |            .   |
   |          .     |
   |       TER      |
   |      .         |
   v    .           v
PLANTER           PAINS
   |    .           |
   |      .         |
   |       LANT     |
   |          .     |
   v            .   v
  PER             PLANTAINS
   |            .   |
   |          .     |
   |       TAIN     |
   |      .         |
   v    .           v
PERTAIN           PLANS

Problem:

The word RETESTED is on the west shore of a river, while the word INGRAIN is on the east shore.
The farmer needs to take his word RETESTED from the west side to the east side.
However, he can only cross the river with one "chunk" at a time,
and the words on both shores must be valid words at every intermediate step.