{ "data": { "question": { "questionId": "3842", "questionFrontendId": "3559", "categoryTitle": "Algorithms", "boundTopicId": 3683573, "title": "Number of Ways to Assign Edge Weights II", "titleSlug": "number-of-ways-to-assign-edge-weights-ii", "content": "
There is an undirected tree with n nodes labeled from 1 to n, rooted at node 1. The tree is represented by a 2D integer array edges of length n - 1, where edges[i] = [ui, vi] indicates that there is an edge between nodes ui and vi.
Initially, all edges have a weight of 0. You must assign each edge a weight of either 1 or 2.
\n\nThe cost of a path between any two nodes u and v is the total weight of all edges in the path connecting them.
You are given a 2D integer array queries. For each queries[i] = [ui, vi], determine the number of ways to assign weights to edges in the path such that the cost of the path between ui and vi is odd.
Return an array answer, where answer[i] is the number of valid assignments for queries[i].
Since the answer may be large, apply modulo 109 + 7 to each answer[i].
Note: For each query, disregard all edges not in the path between node ui and vi.
\n
Example 1:
\n\n
Input: edges = [[1,2]], queries = [[1,1],[1,2]]
\n\nOutput: [0,1]
\n\nExplanation:
\n\n[1,1]: The path from Node 1 to itself consists of no edges, so the cost is 0. Thus, the number of valid assignments is 0.[1,2]: The path from Node 1 to Node 2 consists of one edge (1 → 2). Assigning weight 1 makes the cost odd, while 2 makes it even. Thus, the number of valid assignments is 1.Example 2:
\n\n
Input: edges = [[1,2],[1,3],[3,4],[3,5]], queries = [[1,4],[3,4],[2,5]]
\n\nOutput: [2,1,4]
\n\nExplanation:
\n\n[1,4]: The path from Node 1 to Node 4 consists of two edges (1 → 3 and 3 → 4). Assigning weights (1,2) or (2,1) results in an odd cost. Thus, the number of valid assignments is 2.[3,4]: The path from Node 3 to Node 4 consists of one edge (3 → 4). Assigning weight 1 makes the cost odd, while 2 makes it even. Thus, the number of valid assignments is 1.[2,5]: The path from Node 2 to Node 5 consists of three edges (2 → 1, 1 → 3, and 3 → 5). Assigning (1,2,2), (2,1,2), (2,2,1), or (1,1,1) makes the cost odd. Thus, the number of valid assignments is 4.\n
Constraints:
\n\n2 <= n <= 105edges.length == n - 1edges[i] == [ui, vi]1 <= queries.length <= 105queries[i] == [ui, vi]1 <= ui, vi <= nedges represents a valid tree.给你一棵有 n 个节点的无向树,节点从 1 到 n 编号,树以节点 1 为根。树由一个长度为 n - 1 的二维整数数组 edges 表示,其中 edges[i] = [ui, vi] 表示在节点 ui 和 vi 之间有一条边。
一开始,所有边的权重为 0。你可以将每条边的权重设为 1 或 2。
\n\n两个节点 u 和 v 之间路径的 代价 是连接它们路径上所有边的权重之和。
给定一个二维整数数组 queries。对于每个 queries[i] = [ui, vi],计算从节点 ui 到 vi 的路径中,使得路径代价为 奇数 的权重分配方式数量。
返回一个数组 answer,其中 answer[i] 表示第 i 个查询的合法赋值方式数量。
由于答案可能很大,请对每个 answer[i] 取模 109 + 7。
注意: 对于每个查询,仅考虑 ui 到 vi 路径上的边,忽略其他边。
\n\n
示例 1:
\n\n
输入: edges = [[1,2]], queries = [[1,1],[1,2]]
\n\n输出: [0,1]
\n\n解释:
\n\n[1,1]:节点 1 到自身没有边,代价为 0,因此合法赋值方式为 0。[1,2]:从节点 1 到节点 2 的路径有一条边(1 → 2)。将权重设为 1 时代价为奇数,设为 2 时为偶数,因此合法赋值方式为 1。示例 2:
\n\n
输入: edges = [[1,2],[1,3],[3,4],[3,5]], queries = [[1,4],[3,4],[2,5]]
\n\n输出: [2,1,4]
\n\n解释:
\n\n[1,4]:路径为两条边(1 → 3 和 3 → 4),(1,2) 或 (2,1) 的组合会使代价为奇数,共 2 种。[3,4]:路径为一条边(3 → 4),仅权重为 1 时代价为奇数,共 1 种。[2,5]:路径为三条边(2 → 1 → 3 → 5),组合 (1,2,2)、(2,1,2)、(2,2,1)、(1,1,1) 均为奇数代价,共 4 种。\n\n
提示:
\n\n2 <= n <= 105edges.length == n - 1edges[i] == [ui, vi]1 <= queries.length <= 105queries[i] == [ui, vi]1 <= ui, vi <= nedges 表示一棵合法的树。chainLength and sumParity.",
"Use Lowest Common Ancestor to find the distance between any two nodes quickly in O(logn)."
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