Top 150 Interview Questions P26 Remove Duplicates from Sorted Array

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Timeline

Timeline

2025-09-28

init

std::unique

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Problem:

P26 Remove Duplicates from Sorted Array

https://leetcode.cn/problems/remove-duplicates-from-sorted-array/description/?envType=study-plan-v2&envId=top-interview-150

std::unique is a C++ function in it. It does not actually delete elements in the container, but moves adjacent duplicate elements to the back, and returns an iterator pointing to the new logical end. Combined with erase, it can remove duplicate elements.

#include <algorithm>
#include <vector>
using std::vector;

class Solution {
public:
    int removeDuplicates(vector<int>& nums) {
        nums.erase(std::unique(nums.begin(),nums.end()),nums.end());
        return nums.size();
    }
};

Classic fast-slow pointer solution: the fast pointer represents the index position reached while traversing the array, and the slow pointer represents the index position where the next different element should be filled. Initially, both pointers point to index 1.

class Solution {
public:
    int removeDuplicates(vector<int>& nums) {
        int n = nums.size();
        if (n == 0) {
            return 0;
        }
        int fast = 1, slow = 1;
        while (fast < n) {
            if (nums[fast] != nums[fast - 1]) {
                nums[slow] = nums[fast];
                ++slow;
            }
            ++fast;
        }
        return slow;
    }
};