CODEWITHSUNDEEP
javascriptarraysfor-loopobject
Titan619
Titan619

Reputation: 11

Counting Duplicate elements in an array: Javascript

Could someone please look over my code and explain why my return value = 3 when it should be 2? The object has the correct count {1: 2, 2: 3, 3: 1, 4: 1, 5: 1}. Only two values are >= 2.

  function countDuplicates(arr) {
    let dupNums = {};
    let count = 0;
    ​
    for (let i=0; i<arr.length; i++) {
    ​
        if (dupNums[arr[i]] === undefined) {
            dupNums[arr[i]] = 0;
        }
    ​
        if (dupNums[arr[i]] !== undefined) {
            dupNums[arr[i]] += 1;
        }
    ​
        if (dupNums[arr[i]] >= 2) {
            count++;
        }
    }
    return count; 
    }
    console.log(countDuplicates([1,2,1,3,2,4,5,2]));

Upvotes: 0

Views: 63

Answers (2)

Siva Kondapi Venkata
Siva Kondapi Venkata

Reputation: 11001

Use one Set to track dup nums and another Set for tracking count. Following should work for you scenario.

function countDuplicates(arr) {
  const dupNums = new Set();
  const countSet = new Set();

  arr.forEach((num) =>
    dupNums.has(num) ? countSet.add(num) : dupNums.add(num)
  );

  return countSet.size;
}
console.log(countDuplicates([1, 2, 1, 3, 2, 4, 5, 2]));

Upvotes: 1

CertainPerformance
CertainPerformance

Reputation: 370679

You have three 2s and two 1s. Each time a duplicate is found, count gets incremented.

Iterate over the values of the object afterwards instead, and count up the number of values which are >= 2:

function countDuplicates(arr) {
  const dupNums = {};
  for (const num of arr) {
    dupNums[num] = (dupNums[num] || 0) + 1;
  };
  return Object.values(dupNums)
    .filter(num => num >= 2)
    .length;
}
console.log(countDuplicates([1, 2, 1, 3, 2, 4, 5, 2]));

or with reduce:

function countDuplicates(arr) {
  const dupNums = {};
  for (const num of arr) {
    dupNums[num] = (dupNums[num] || 0) + 1;
  };
  return Object.values(dupNums)
    .reduce((a, num) => a + (num >= 2), 0)
}
console.log(countDuplicates([1, 2, 1, 3, 2, 4, 5, 2]));

Upvotes: 1

Related Questions