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26. [Array]Remove 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.

Example 2:

Given nums = [0,0,1,1,1,2,2,3,3,4],

Your function should return length = 5, with the first five elements of nums being modified to 0, 1, 2, 3, and 4 respectively.

It doesn't matter what values are set beyond the returned length.

python solution

class Solution:
    def removeDuplicates(self, nums: List[int]) -> int:
        i = 0
        n = len(nums)
        while i < n-1:
            if nums[i]==nums[i+1]:
                nums.pop(i+1)
                n -= 1
            else:
                i += 1
        return len(nums)

27. [Array]Remove Element

Given an array nums and a value val, remove all instances of that value in-place 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. The order of elements can be changed. It doesn’t matter what you leave beyond the new length.

Example 1:

Given nums = [3,2,2,3], val = 3,

Your function should return length = 2, with the first two elements of nums being 2.

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

Example 2:

Given nums = [0,1,2,2,3,0,4,2], val = 2,

Your function should return length = 5, with the first five elements of nums containing 0, 1, 3, 0, and 4.

Note that the order of those five elements can be arbitrary.

It doesn't matter what values are set beyond the returned length.

python solution 1:

class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        n = len(nums)
        i = 0
        while i<n:
            if nums[i] == val:
                nums.pop(i)
                n -= 1
            else:
                i += 1
        return len(nums)

Note:

上述方法就是和26题相似,删去符合条件的值,还可以利用双指针法:

python solution 2:

class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        n = len(nums)
        i = 0
        for j in range(n):
            if nums[j] == val:
                continue
            else:
                nums[i]=nums[j]
                i += 1
        return i