8.11笔记

80. 删除排序数组中的重复项 II

class Solution(object):
    def removeDuplicates(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        i = 0
        for num in nums:
            if i < 2 or num != nums[i-2]:
                nums[i] = num
                i += 1
        return i

144. 二叉树的前序遍历（递归+非递归）

#递归版本
class Solution(object):
    def preorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        res = []
        self.dfs(root,res)
        return res
    def dfs(self,root,res):
        if not root:
            return 
        res.append(root.val)
        self.dfs(root.left,res)
        self.dfs(root.right,res)
#非递归
class Solution(object):
    def preorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root:
            return []
        res = []
        stack = [root]
        while stack:
            a = stack.pop()
            if a.right:
                stack.append(a.right)
            if a.left:
                stack.append(a.left)
            res.append(a.val)
        return res