leetcode-12双周赛-1245-树的直径

题目描述：

方法一：深度优先：

class Solution:
    def treeDiameter(self, edges: List[List[int]]) -> int:
        adjacency = collections.defaultdict(set)
        for i,j in edges:
            adjacency[i].add(j)
            adjacency[j].add(i)
        memo = {}
        def dfs(i,j):
            if (i,j) in memo:
                return memo[i,j]
            longest = 0
            for k in adjacency[j]:
                if k == i:continue
                longest = max(longest,dfs(j,k))
            memo[(i,j)] = longest + 1
            return memo[(i,j)]
        for i,j in edges:
            dfs(i,j)
            dfs(j,i)
        return max(memo[(i,j)]+memo[(j,i)]-1 for i,j in edges)

方法二：广度优先

class Solution:
    def treeDiameter(self, edges: List[List[int]]) -> int:
        adjacency = collections.defaultdict(set)
        for i,j in edges:
            adjacency[i].add(j)
            adjacency[j].add(i)
        def bfs(node):
            queue = collections.deque()
            queue.append((node,0))
            memo = {node}
            while queue:
                n,long = queue.popleft()
                for nei in adjacency[n]:
                    if nei not in memo:
                        memo.add(nei)
                        queue.append((nei,long+1))
            return n,long

        far,long = bfs(0)
        far2,longest = bfs(far)
        return longest