1426. Counting Elements

https://leetcode.com/problems/counting-elements

Description

Given an integer array arr, count how many elements x there are, such that x + 1 is also in arr. If there are duplicates in arr, count them separately.

Example 1:

**Input:** arr = [1,2,3]
**Output:** 2
**Explanation:** 1 and 2 are counted cause 2 and 3 are in arr.

Example 2:

**Input:** arr = [1,1,3,3,5,5,7,7]
**Output:** 0
**Explanation:** No numbers are counted, cause there's no 2, 4, 6, or 8 in arr.

Example 3:

**Input:** arr = [1,3,2,3,5,0]
**Output:** 3
**Explanation:** 0, 1 and 2 are counted cause 1, 2 and 3 are in arr.

Example 4:

**Input:** arr = [1,1,2,2]
**Output:** 2
**Explanation:** Two 1s are counted cause 2 is in arr.

Example 5:

**Input:** arr = [1,1,2]
**Output:** 2
**Explanation:** Both 1s are counted because 2 is in the array.

Constraints:

• 1 <= arr.length <= 1000

• 0 <= arr[i] <= 1000

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