JavaScript In-Place Array Manipulation

In this article, we will explore a JavaScript function that removes duplicate numbers from a given sorted array in place. This means that the function modifies the original array directly, without creating a new array.

var removeDuplicates = function (nums) {
  if (nums.length === 0) {
    return 0;
  }
  let count = 1;
  for (let i = 1; i < nums.length; i++) {
    if (nums[i] !== nums[i - 1]) {
      nums[count] = nums[i];
      count++;
    }
  }
  nums.length = count;
  return nums;
  // return the array or the array length
};
removeDuplicates([0, 0, 1, 1, 1, 2, 2, 3, 3, 4])

Given the input array [0, 0, 1, 1, 1, 2, 2, 3, 3, 4], here's the detailed execution:

1. Initial state:

   • nums: [0, 0, 1, 1, 1, 2, 2, 3, 3, 4]
   • count: 1

2. Iteration 1 (i = 1):

   • nums[i]: 0
   • nums[i - 1]: 0
   • Since nums[i] is equal to nums[i - 1], it means the current element is a duplicate.
   • No modifications are made.

3. Iteration 2 (i = 2):

   • nums[i]: 1
   • nums[i - 1]: 0
   • Since nums[i] is not equal to nums[i - 1], it means the current element is unique.
   • The unique element (1) is assigned to nums[count] (index 1) and count is incremented.
   • Modified nums: [0, 1, 1, 1, 1, 2, 2, 3, 3, 4]
   • Updated count: 2

4. Iteration 3 (i = 3):

   • nums[i]: 1
   • nums[i - 1]: 1
   • Since nums[i] is equal to nums[i - 1], it means the current element is a duplicate.
   • No modifications are made.

5. Iteration 4 (i = 4):

   • nums[i]: 1
   • nums[i - 1]: 1
   • Since nums[i] is equal to nums[i - 1], it means the current element is a duplicate.
   • No modifications are made.

6. Iteration 5 (i = 5):

   • nums[i]: 2
   • nums[i - 1]: 1
   • Since nums[i] is not equal to nums[i - 1], it means the current element is unique.
   • The unique element (2) is assigned to nums[count] (index 2) and count is incremented.
   • Modified nums: [0, 1, 2, 1, 1, 2, 2, 3, 3, 4]
   • Updated count: 3

7. Iteration 6 (i = 6):

   • nums[i]: 2
   • nums[i - 1]: 1
   • Since nums[i] is equal to nums[i - 1], it means the current element is a duplicate.
   • No modifications are made.

8. Iteration 7 (i = 7):

   • nums[i]: 3
   • nums[i - 1]: 2
   • Since nums[i] is not equal to nums[i - 1], it means the current element is unique.
   • The unique element (3) is assigned to nums[count] (index 3) and count is incremented.
   • Modified nums: [0, 1, 2, 3, 1, 2, 2, 3, 3, 4]
   • Updated count: 4

9. Iteration 8 (i = 8):

   • nums[i]: 3
   • nums[i - 1]: 3
   • Since nums[i] is equal to nums[i - 1], it means the current element is a duplicate.
   • No modifications are made.

10. Iteration 9 (i = 9):

    • nums[i]: 4
    • nums[i - 1]: 3
    • Since nums[i] is not equal to nums[i - 1], it means the current element is unique.
    • The unique element (4) is assigned to nums[count] (index 4) and count is incremented.
    • Modified nums: [0, 1, 2, 3, 4, 2, 2, 3, 3, 4]
    • Updated count: 5

11. The loop ends since we have iterated through all elements of the array.

12. The nums.length property is set to count to remove any excess elements.

    • Final nums: [0, 1, 2, 3, 4]

The modified nums array contains only the unique elements [0, 1, 2, 3, 4].