403.Frog Jump
===
###### tags: `Hard` `Array` `DP`
[403. Frog Jump](https://leetcode.com/problems/frog-jump/)
### 題目描述
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.
### 範例
**Example 1:**
```
Input: stones = [0,1,3,5,6,8,12,17]
Output: true
Explanation: 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: false
Explanation: 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.
### 解答
### Reference
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