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Leetcode 26: Remove Duplicates from Sorted Array

DevGod
DevGod
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Question

In this Leetcode problem, we are given a pre-sorted, strictly increasing array of numbers and must remove adjacent duplicate values in-place. However, Leetcode includes a custom judge for this problem that verifies whether the array is modified in-place. For example, we do NOT want to initialize a new array to solve this problem, we want to solve this problem in-place using the original array. Another requirement of the custom judge for this question is to return K. The value K represents the amount of unique values we have after removing adjacent duplicates from the given array.

Solving

To solve this problem, I used a two pointer approach to modify the array in-place and keep track of unique values, K. I implement a for-loop that moves my right pointer R across the array. Every time nums[R] and nums[R+1] don’t equal each other, I have found a new unique value. Anytime my left pointer array element updates, I move the L one space. The right pointer, R and R+1 continue to move forwards until they reach the end of the given array.

In other words, my right pointer R is used in a sliding window style traversal to check all adjacent duplicate values in the array. Meanwhile, my left pointer L is strictly used to update positions in the left of the array, as I find unique values. Additionally, my left pointer L also keeps track of the amount of unique values that I have encountered in the given array. This is because every time I modify the position of left pointer L, it increments by one, which effectively keeps a running score of every time I updated the left section of the array.

Lastly, although the two-pointer solution does not remove the remaining “junk” values in the right section of the array, the custom judge only checks the first K elements for correctness.

TLDR

I used a two pointer approach to modify the given array in-place to hold the unique values in the left section of the array, satisfying the custom Leetcode judge requirements.

/**
 * @param {number[]} nums
 * @return {number}
 */
var removeDuplicates = function(nums) {
    let L = 1;
    for(let R = 0; R < nums.length-1; R++ ){
        if(nums[R+1] !== nums[R]){
        nums[L++] = nums[R+1];
        }
    }
    return L;
};