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2246. Longest Path With Different Adjacent Characters
You are given a tree (i.e. a connected, undirected graph that has no cycles) rooted at node 0
consisting of n
nodes numbered from 0
to n - 1
. The tree is represented by a 0-indexed array parent
of size n
, where parent[i]
is the parent of node i
. Since node 0
is the root, parent[0] == -1
.
You are also given a string s
of length n
, where s[i]
is the character assigned to node i
.
Return the length of the longest path in the tree such that no pair of adjacent nodes on the path have the same character assigned to them.
Example 1:
Input: parent = [-1,0,0,1,1,2], s = "abacbe" Output: 3 Explanation: The longest path where each two adjacent nodes have different characters in the tree is the path: 0 -> 1 -> 3. The length of this path is 3, so 3 is returned. It can be proven that there is no longer path that satisfies the conditions.
Example 2:
Input: parent = [-1,0,0,0], s = "aabc" Output: 3 Explanation: The longest path where each two adjacent nodes have different characters is the path: 2 -> 0 -> 3. The length of this path is 3, so 3 is returned.
Constraints:
n == parent.length == s.length
1 <= n <= 105
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from collections import defaultdict
class Solution:
def longestPath(self, parent: List[int], s: str) -> int:
graph = defaultdict(list)
for idx, p in enumerate(parent):
if p == -1: continue
graph[p].append(idx)
pathlen = 0
def dfs(curr):
nonlocal pathlen
max1 = max2 = 0
for nxt in graph[curr]:
childlen = dfs(nxt)
if s[nxt] != s[curr]:
if childlen > max1:
max1, max2 = childlen, max1
elif childlen > max2:
max2 = childlen
pathlen = max(pathlen, max1+max2+1)
return max1+1
dfs(0)
return pathlen