0.17 技巧

[136. 只出现一次的数字](https://leetcode.cn/problems/single-number/?envType=study-plan-v2&envId=top-100-liked)
```python
class Solution:
    def singleNumber(self, nums: List[int]) -> int:
        result = 0
        for num in nums:
            result ^= num
        return result
```
[169. 多数元素](https://leetcode.cn/problems/majority-element/?envType=study-plan-v2&envId=top-100-liked)
```python
class Solution:
    def majorityElement(self, nums: List[int]) -> int:
        candidate = None
        count = 0
        for num in nums:
            if count == 0:
                candidate = num
            count += 1 if num == candidate else -1
        return candidate
```
[75. 颜色分类](https://leetcode.cn/problems/sort-colors/?envType=study-plan-v2&envId=top-100-liked)
```python
class Solution:
    def sortColors(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        left, mid, right = 0, 0, len(nums) - 1
        while mid <= right:
            if nums[mid] == 0:
                nums[left], nums[mid] = nums[mid], nums[left]
                left += 1
                mid += 1
            elif nums[mid] == 1:
                mid += 1
            else:
                nums[right], nums[mid] = nums[mid], nums[right]
                right -= 1

```
[31. 下一个排列](https://leetcode.cn/problems/next-permutation/?envType=study-plan-v2&envId=top-100-liked)
```python
class Solution:
    def nextPermutation(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        n = len(nums)
        i = n - 2
        while i >= 0 and nums[i] >= nums[i + 1]:
            i -= 1
        if i < 0:
            nums.reverse()
            return
        j = n - 1
        while j > i and nums[j] <= nums[i]:
            j -= 1
        nums[i], nums[j] = nums[j], nums[i]
        left, right = i + 1, n - 1
        while left < right:
            nums[left], nums[right] = nums[right], nums[left]
            left += 1
            right -= 1

```
[287. 寻找重复数](https://leetcode.cn/problems/find-the-duplicate-number/?envType=study-plan-v2&envId=top-100-liked)
```python
class Solution:
    def findDuplicate(self, nums: List[int]) -> int:
        st = set()
        for num in nums:
            if num in st:
                return num
            st.add(num)
```
```python
class Solution:
    def findDuplicate(self, nums: List[int]) -> int:
        slow = fast = nums[0]
        while True:
            slow = nums[slow]
            fast = nums[nums[fast]]
            if slow == fast:
                break
        fast = nums[0]
        while slow != fast:
            slow = nums[slow]
            fast = nums[fast]
        return slow
```