403. Frog Jump

Hard

3.8K

191

A frog is crossing a river. The river is divided into some number of 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 can cross the river by landing on the last stone. Initially, the frog is on the first stone and assumes the first jump must be `1`

unit.

If the frog's last jump was `k`

units, its next jump must be either `k - 1`

, `k`

, or `k + 1`

units. The frog can only jump in the forward direction.

**Example 1:**

Input:stones = [0,1,3,5,6,8,12,17]Output:trueExplanation:The frog can jump to the last stone by jumping 1 unit to the 2nd stone, then 2 units to the 3rd stone, then 2 units to the 4th stone, then 3 units to the 6th stone, 4 units to the 7th stone, and 5 units to the 8th stone.

**Example 2:**

Input:stones = [0,1,2,3,4,8,9,11]Output:falseExplanation:There is no way to jump to the last stone as the gap between the 5th and 6th stone is too large.

**Constraints:**

`2 <= stones.length <= 2000`

`0 <= stones[i] <= 2`

^{31}- 1`stones[0] == 0`

`stones`

is sorted in a strictly increasing order.

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