Longest path with different adjacent characters

We will create a tree from the edges list. Then we will start DFS from starting node 0. Then we will calculate the longest path in the subtree of each node. Finally we will return the longest path in the subtree of each node.

class Solution:
    def longestPath(self, parent: List[int], s: str) -> int:
        tree = defaultdict(list)
        for end, start in enumerate(parent):
            tree[start].append(end)

        self.res = 1

        def dfs(node):
            max1 = max2 = 0
            for nei in tree[node]:
                neiL = dfs(nei)
                if s[nei] != s[node]:
                    if neiL > max1:
                        max2 = max1
                        max1 = neiL
                    elif neiL > max2:
                        max2 = neiL
            self.res = max(self.res, max1+max2+1)

            return max1+1

        dfs(0)
        return self.res

Time complexity: O(n)
Space complexity: O(n)