738. 单调递增的数字

发现第一位变小了其他的迅速变9

class Solution:
    def monotoneIncreasingDigits(self, n: int) -> int:
        strn=list(str(n))
        for i in range(len(strn)-1,0,-1):
            if strn[i-1]>strn[i]:
                strn[i-1]=str(int(strn[i-1])-1)
                for j in range(i,len(strn)):
                    strn[j]='9'
        return int(''.join(strn))

968. 监控二叉树

res是list才能传对象

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def minCameraCover(self, root: Optional[TreeNode]) -> int:
        res=[0]
        if self.tree(root,res)==0:
            res[0]+=1
        return res[0]
    def tree(self,cur,res):
        if not cur:
            return 2
        left=self.tree(cur.left,res)
        right=self.tree(cur.right,res)
        if left==2 and right==2:
            return 0
        elif left==0 or right==0:
            res[0]+=1
            return 1
        # if left==1 or right==1:
        else:
            return 2