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g2101_2200.s2145_count_the_hidden_sequences.readme.md Maven / Gradle / Ivy

2145\. Count the Hidden Sequences

Medium

You are given a **0-indexed** array of `n` integers `differences`, which describes the **differences** between each pair of **consecutive** integers of a **hidden** sequence of length `(n + 1)`. More formally, call the hidden sequence `hidden`, then we have that `differences[i] = hidden[i + 1] - hidden[i]`.

You are further given two integers `lower` and `upper` that describe the **inclusive** range of values `[lower, upper]` that the hidden sequence can contain.

*   For example, given `differences = [1, -3, 4]`, `lower = 1`, `upper = 6`, the hidden sequence is a sequence of length `4` whose elements are in between `1` and `6` (**inclusive**).
    *   `[3, 4, 1, 5]` and `[4, 5, 2, 6]` are possible hidden sequences.
    *   `[5, 6, 3, 7]` is not possible since it contains an element greater than `6`.
    *   `[1, 2, 3, 4]` is not possible since the differences are not correct.

Return _the number of **possible** hidden sequences there are._ If there are no possible sequences, return `0`.

**Example 1:**

**Input:** differences = [1,-3,4], lower = 1, upper = 6

**Output:** 2

**Explanation:** The possible hidden sequences are: 

- [3, 4, 1, 5] 

- [4, 5, 2, 6] 
  
Thus, we return 2.

**Example 2:**

**Input:** differences = [3,-4,5,1,-2], lower = -4, upper = 5

**Output:** 4

**Explanation:** The possible hidden sequences are: 

- [-3, 0, -4, 1, 2, 0] 

- [-2, 1, -3, 2, 3, 1] 

- [-1, 2, -2, 3, 4, 2] 

- [0, 3, -1, 4, 5, 3] 
  
Thus, we return 4.

**Example 3:**

**Input:** differences = [4,-7,2], lower = 3, upper = 6

**Output:** 0

**Explanation:** There are no possible hidden sequences. Thus, we return 0.

**Constraints:**

*   `n == differences.length`
*   1 <= n <= 105
*   -105 <= differences[i] <= 105
*   -105 <= lower <= upper <= 105