Counting Elements.cpp

/*
 Counting Elements
Solution
Given an integer array arr, count element x such that x + 1 is also in arr.

If there're duplicates in arr, count them seperately.

 

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.
*/

class Solution {
public:
    int countElements(vector<int>& arr) {
        map<int,int> m;
        for(long long int i=0;i<arr.size();i++)
        {
            m[arr[i]] = 1;
        }
        long long int sum =0;
        for(long long int i=0;i<arr.size();i++)
        {
            if(m[arr[i]+1]==1)
            {
                sum += 1;
            }
        }
        return sum;
    }
};