counting elemets frequency using map code example

Example 1: Count frequency of array elements js

var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4]

const map = arr.reduce((acc, e) => acc.set(e, (acc.get(e) || 0) + 1), new Map());

console.info([...map.keys()]) // to get unique elements
console.info([...map.values()]) // to get the occurrences
console.info([...map.entries()]) // to get the pairs [element, frequency]

Example 2: mark occurances of elements in array cpp

int sumOfDistinct(int a[], int n){
  	int sum = 0; 
    for (int i = 0; i < n; i++) { 
      	 // If element appears first time 
        if (a[abs(a[i]) - 1] >= 0) { 
            sum += abs(a[i]); 
            a[abs(a[i]) - 1] *= -1; 
        } 
    } 
    return sum;