0.2 双指针

[125. 验证回文串](https://leetcode.cn/problems/valid-palindrome/?envType=study-plan-v2&envId=top-interview-150)
```python
class Solution:
    def isPalindrome(self, s: str) -> bool:
        n = len(s)
        left, right = 0, n - 1
        while left <= right:
            if not s[left].isalnum():
                left += 1
            elif not s[right].isalnum():
                right -= 1
            else:
                if s[left].lower() != s[right].lower():
                    return False
                else:
                    left += 1
                    right -= 1
        return True

```
[392. 判断子序列](https://leetcode.cn/problems/is-subsequence/description/?envType=study-plan-v2&envId=top-interview-150)
```python
class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        i = j = 0
        while i < len(s) and j < len(t):
            if s[i] == t[j]:
                i += 1
            j += 1
        return i == len(s)
```
[167. 两数之和 II - 输入有序数组](https://leetcode.cn/problems/two-sum-ii-input-array-is-sorted/description/?envType=study-plan-v2&envId=top-interview-150)
```python
class Solution:
    def twoSum(self, numbers: List[int], target: int) -> List[int]:
        n = len(numbers)
        left, right = 0, n - 1
        while left <= right:
            x = numbers[left] + numbers[right]
            if x == target:
                return [left + 1, right + 1]
            elif x > target:
                right -= 1
            else:
                left += 1
```
[11. 盛最多水的容器](https://leetcode.cn/problems/container-with-most-water/description/?envType=study-plan-v2&envId=top-interview-150)
```python
class Solution:
    def maxArea(self, height: List[int]) -> int:
        n = len(height)
        left, right = 0, n - 1
        res = 0
        while left <= right:
            h = min(height[left], height[right])
            w = right - left
            res = max(res, h * w)
            if height[left] < height[right]:
                left += 1
            else:
                right -= 1
        return res

```
[15. 三数之和](https://leetcode.cn/problems/3sum/?envType=study-plan-v2&envId=top-interview-150)
```python
class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:
        n = len(nums)
        nums.sort()
        res = []
        for i in range(n - 2):
            if i > 0 and nums[i] == nums[i - 1]:
                continue
            if nums[i] > 0:
                break
            j, k = i + 1, n - 1
            while j < k:
                s = nums[i] + nums[j] + nums[k]
                if s < 0:
                    j += 1
                    while j < k and nums[j] == nums[j - 1]:
                        j += 1
                elif s > 0:
                    k -= 1
                    while j < k and nums[k] == nums[k + 1]:
                        k -= 1
                else:
                    res.append([nums[i], nums[j], nums[k]])
                    j += 1
                    k -= 1
                    while j < k and nums[j] == nums[j - 1]:
                        j += 1
                    while j < k and nums[k] == nums[k + 1]:
                        k -= 1
        return res
```