27. 移除元素

思路见注释。
 1 class Solution(object):
 2     def removeElement(self, nums, val):
 3         """
 4         :type nums: List[int]
 5         :type val: int
 6         :rtype: int
 7         """
 8         if len(nums) == 0:
 9             return 0
10         # 双指针
11         i, j = 0, len(nums) - 1
12         while i < j:
13             # j指向的等于val，j前移
14             if nums[j] == val:
15                 j -= 1
16                 continue
17             # 如果i指向的等于val，交换i和j的值，j前移
18             if nums[i] == val:
19                 nums[i], nums[j] = nums[j], nums[i]
20                 j -= 1
21             # i每一趟都后移
22             i += 1
23         print(nums, i, j)
24         if nums[i] == val:
25             return len(nums[:i])
26         else:
27             return len(nums[:i]) + 1
28 
29 if __name__ == '__main__':
30     solution = Solution()
31     print(solution.removeElement(nums=[0, 1, 2, 2, 3, 2, 4, 2, 5], val=2))
32     print(solution.removeElement(nums=[], val=5))