A frog is crossing a river. The river is divided into x units and at each unit there may or may not exist a stone. The frog can jump on a stone, but it must not jump into the water.
Given a list of stones’ positions (in units) in sorted ascending order, determine if the frog is able to cross the river by landing on the last stone. Initially, the frog is on the first stone and assume the first jump must be 1 unit.
If the frog’s last jump was k units, then its next jump must be either k - 1, k, or k + 1 units. Note that the frog can only jump in the forward direction.
The number of stones is ≥ 2 and is < 1,100.
Each stone’s position will be a non-negative integer < 231.
The first stone’s position is always 0.
There are a total of8 stones.
The first stone atthe0th unit, second stone atthe1st unit,
third stone atthe3rd unit, and so on...
The last stone atthe17th unit.
Return true. The frog can jump tothelast stone by jumping
1 unit tothe2nd stone, then2 units tothe3rd stone, then
2 units tothe4th stone, then3 units tothe6th stone,
4 units tothe7th stone, and5 units tothe8th stone.
Return false. There is no way to jump to the last stone as
the gap between the 5th and 6th stone is too large.