Mayank Arora

Posted on

# 26. Remove Duplicates from Sorted Array [Leetcode][C++]

All suggestions are welcome. Please upvote if you like it. Thank you.

Leetcode Problem Link: 26. Remove Duplicates from Sorted Array

Brute Force Solution:

``````class Solution {
public:
int removeDuplicates(vector<int>& nums) {
// Brute Force Solution
// Time O(NlogN) as map insertion takes O(logN) time and loop runs for N such iterations. Auxiliary Space O(N)
vector<int> ans;
map<int,int> mp;
for(int i = 0; i < nums.size() ; i++){
if(mp[nums[i]]==0)
ans.push_back(nums[i]); // ans vector stores unique elements based on their first occurence in nums vector
mp[nums[i]]++; // mp stores frequency of each unique element in nums vector
}
nums = ans; // ans vector has all unique elements in ascending order.
// These unique elements are overwritten on initial indices of nums array.
return ans.size();
}
};

``````

Optimal Solution:

``````class Solution {
public:
int removeDuplicates(vector<int>& nums) {
// Optimal Solution
// Time O(N) & Auxiliary Space O(1)
// Two Pointer Method
int len=nums.size();
if(len==0)
return 0;
int p1=0;
for(int p2=1;p2<len;p2++){
if(nums[p1]!=nums[p2]){
// If elements at p1 & p2 not equal, increment p1 and copy
// nums[p2] to nums[p1] so as to concentrate all unique
// elements in ascending order at the initial indices of the vector
p1++;
nums[p1]=nums[p2];
}
}
// p1 location is the final indice of the
// unique element subarray at the beginning of nums vector
return p1+1;
}
};

``````

All suggestions are welcome. Please upvote if you like it. Thank you.