Watch 10 video solutions for Counting Elements, a easy level problem involving Array, Hash Table. This walkthrough by NeetCode has 132,421 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
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 is no 2, 4, 6, or 8 in arr.
Constraints:
1 <= arr.length <= 10000 <= arr[i] <= 1000