26. Remove Duplicates from Sorted Array

描述

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.

Clarification:

Confused why the returned value is an integer but your answer is an array?

Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.

Internally you can think of this:

// nums is passed in by reference. (i.e., without making a copy)
int len = removeDuplicates(nums);

// any modification to nums in your function would be known by the caller.
// using the length returned by your function, it prints the first len elements.
for (int i = 0; i < len; i++) {
    print(nums[i]);
}

解法

思路借鉴快速排序的 partition 过程，使用两根指针， i 用于保存当前可以被替换的位置，j 表示下一个与当前值不同的数字。

class Solution:
    def removeDuplicates(self, nums: List[int]) -> int:
        if not nums:
            return 0

        i = 0
        for j in range(1, len(nums)):
            if nums[i] != nums[j]:
                i += 1
                nums[i] = nums[j]

        return i + 1