# Remove Duplicates in Sorted Array (I II)

xiaoxiao2021-02-28  70

26Remove Duplicates from Sorted Array

Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length.

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

Example 1:

Given nums = [1,1,2], Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively.

It doesn't matter what you leave beyond the returned length.

int removeDuplicates(vector<int>& nums) { if (nums.size() == 0) { return 0; } int i = 0, j = 0, rightBound = (int)nums.size() - 1; nums.push_back(nums[0] - 1); while (j <= rightBound) { while (j <= rightBound && nums[j] != nums[j+1]) { nums[i++] = nums[j++]; } while (j <= rightBound && nums[j] == nums[j+1]) { j++; } } return i; }

int removeDuplicates(vector<int>& nums) { int i = 0; for (int n : nums) if (!i || n > nums[i-1]) nums[i++] = n; return i; }

80Remove Duplicates from Sorted Array II

Given a sorted array nums, remove the duplicates in-place such that duplicates appeared at most twice and return the new length.

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

Example 1:

Given nums = [1,1,1,2,2,3],Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3 respectively.

It doesn't matter what you leave beyond the returned length.

// Idea: two pointers // j runs faster then i. i tracks the right-side boudary of result array, j runs ahead to move valid nums to nums[i] // [0, 0, 1, 3, 3, 7, 7, 7, 7, 8, 9, 10, ...] // i j int removeDuplicates(vector<int>& nums) { if (nums.size() == 0) { return 0; } int i = 0, j = 0, rightBound = (int)nums.size() - 1; nums.push_back(nums[0] - 1); while (j <= rightBound) { while (j <= rightBound && nums[j] != nums[j+1]) { nums[i++] = nums[j++]; } if (j < rightBound) { nums[i++] = nums[j++]; } while (j <= rightBound && nums[j] == nums[j+1]) { j++; } } return i; }

int removeDuplicates(vector<int>& nums) { int i = 0; for (int n : nums) if (i < 2 || n > nums[i-2]) nums[i++] = n; return i; }