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HTML

              
                
              
            
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CSS

              
                
              
            
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JS

              
                  var firstArray = [2, 2, 4, 1];
  var secondArray = [1, 2, 0, 2];

  intersection(firstArray, secondArray); // [1, 2]

  function intersection(firstArray, secondArray) {
    // The logic here is to create a hashmap with the elements of the firstArray as the keys.
    // After that, you can use the hashmap's O(1) look up time to check if the element exists in the hash
    // If it does exist, add that element to the new array.

    var hashmap = {};
    var intersectionArray = [];

    firstArray.forEach(function(element) {
      hashmap[element] = 1;
    });

    // Since we only want to push unique elements in our case... we can implement a counter to keep track of what we already added
    secondArray.forEach(function(element) {
      if (hashmap[element] === 1) {
        intersectionArray.push(element);
        hashmap[element]++;
      }
    });

    return intersectionArray;

    // Time complexity O(n), Space complexity O(n)
  }

              
            
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