RemoveElement.java

package by.andd3dfx.common;

/**
 * <pre>
 * <a href="https://leetcode.com/problems/remove-element/">Task description</a>
 *
 * Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the
 * elements may be changed. Then return the number of elements in nums which are not equal to val.
 *
 * Consider the number of elements in nums which are not equal to val be k, to get accepted, you need to do the
 * following things:
 * - Change the array nums such that the first k elements of nums contain the elements which are not equal to val.
 * The remaining elements of nums are not important as well as the size of nums.
 * - Return k.
 *
 * Example 1:
 *
 * Input: nums = [3,2,2,3], val = 3
 * Output: 2, nums = [2,2,_,_]
 * Explanation: Your function should return k = 2, with the first two elements of nums being 2.
 * It does not matter what you leave beyond the returned k (hence they are underscores).
 *
 * Example 2:
 *
 * Input: nums = [0,1,2,2,3,0,4,2], val = 2
 * Output: 5, nums = [0,1,4,0,3,_,_,_]
 * Explanation: Your function should return k = 5, with the first five elements of nums containing 0, 0, 1, 3, and 4.
 * Note that the five elements can be returned in any order.
 * It does not matter what you leave beyond the returned k (hence they are underscores).
 * </pre>
 *
 * @see <a href="https://youtu.be/ECdosiz1ZPM">Video solution</a>
 */
public class RemoveElement {

    public static int removeElement(int[] nums, int val) {
        var count = nums.length;

        var left = 0;
        var right = 0;
        while (right < nums.length) {
            // Skip all items that equals to `val`
            while (right < nums.length && nums[right] == val) {
                right++;
                count--;
            }

            // Copy from right side to left side all items that not equals to `val`
            // (until we found item equals to `val` or array finished)
            while (right < nums.length && nums[right] != val) {
                nums[left] = nums[right];
                left++;
                right++;
            }
        }

        return count;
    }
}