Multiple Pointers - countUniqueValues

countUniqueValues.js

function countUniqueValues(arr) {
  if (arr.length === 0) {
    return 0;
  }

  let i = 0; // Slow pointer
  for (let j = 1; j < arr.length; j++) {
    if (arr[i] !== arr[j]) {
      i++;
      arr[i] = arr[j];
    }
  }

  return i + 1;
}

This function uses two pointers, where i represents the slow pointer and j represents the fast pointer. The loop iterates through the array, and whenever a unique value is found, the slow pointer is moved, and the unique value is placed at the slow pointer's position in the array. Finally, the count of unique values is given by i + 1. This approach has O(1) space complexity and O(n) time complexity.