8.3笔记

503. 下一个更大元素 II

class Solution:
    def nextGreaterElements(self, nums: List[int]) -> List[int]:
        l = len(nums)
        res = [-1 for _ in range(l)]
        stack = []
        double_nums = nums + nums
        for index,num in enumerate(double_nums):
            while stack and nums[stack[-1]] < num:
                res[stack[-1]] = num
                stack.pop()
            if index < l:
                stack.append(index)
        return res

508. 出现次数最多的子树元素和

class Solution:
    def findFrequentTreeSum(self, root: TreeNode) -> List[int]:
        if not root:
            return []
        d = {}
        self.dfs(root,d)
        k = max(d.values())
        res = []
        for i in d:
            if d[i] == k:
                res.append(i)
        return res

    def dfs(self,root,d):
        if not root:
            return 0
        s = self.dfs(root.left,d) + self.dfs(root.right,d) + root.val
        d[s] = d.get(s,0) + 1
        return s