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

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(); } }; 

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; } };