In order to output all solutions,

just change P from`boolean` to a collection which contains all parent index.

To find all strings break at breakpoint, just using DFS to find out them.

* 10, 7, 3, 0: dog sand cat

* 10, 7, 4, 0: dog and cats

offsets here is 1 larger than the original offset.

So,`7..10` here is to start form the next element, the 8th to the 11th(exclusive).

Luckily, restore the`S[8th..11th]` is just the same as`S[7..10]`,

Because index of S starts from`0`.

* write down thinking