{ "data": { "question": { "questionId": "3307", "questionFrontendId": "3068", "boundTopicId": null, "title": "Find the Maximum Sum of Node Values", "titleSlug": "find-the-maximum-sum-of-node-values", "content": "
There exists an undirected tree with n
nodes numbered 0
to n - 1
. You are given a 0-indexed 2D integer array edges
of length n - 1
, where edges[i] = [ui, vi]
indicates that there is an edge between nodes ui
and vi
in the tree. You are also given a positive integer k
, and a 0-indexed array of non-negative integers nums
of length n
, where nums[i]
represents the value of the node numbered i
.
Alice wants the sum of values of tree nodes to be maximum, for which Alice can perform the following operation any number of times (including zero) on the tree:
\n\n[u, v]
connecting the nodes u
and v
, and update their values as follows:\n\n\tnums[u] = nums[u] XOR k
nums[v] = nums[v] XOR k
Return the maximum possible sum of the values Alice can achieve by performing the operation any number of times.
\n\n\n
Example 1:
\n\n\nInput: nums = [1,2,1], k = 3, edges = [[0,1],[0,2]]\nOutput: 6\nExplanation: Alice can achieve the maximum sum of 6 using a single operation:\n- Choose the edge [0,2]. nums[0] and nums[2] become: 1 XOR 3 = 2, and the array nums becomes: [1,2,1] -> [2,2,2].\nThe total sum of values is 2 + 2 + 2 = 6.\nIt can be shown that 6 is the maximum achievable sum of values.\n\n\n
Example 2:
\n\n\nInput: nums = [2,3], k = 7, edges = [[0,1]]\nOutput: 9\nExplanation: Alice can achieve the maximum sum of 9 using a single operation:\n- Choose the edge [0,1]. nums[0] becomes: 2 XOR 7 = 5 and nums[1] become: 3 XOR 7 = 4, and the array nums becomes: [2,3] -> [5,4].\nThe total sum of values is 5 + 4 = 9.\nIt can be shown that 9 is the maximum achievable sum of values.\n\n\n
Example 3:
\n\n\nInput: nums = [7,7,7,7,7,7], k = 3, edges = [[0,1],[0,2],[0,3],[0,4],[0,5]]\nOutput: 42\nExplanation: The maximum achievable sum is 42 which can be achieved by Alice performing no operations.\n\n\n
\n
Constraints:
\n\n2 <= n == nums.length <= 2 * 104
1 <= k <= 109
0 <= nums[i] <= 109
edges.length == n - 1
edges[i].length == 2
0 <= edges[i][0], edges[i][1] <= n - 1
edges
represent a valid tree.dp[x][c]
be the maximum sum we can get for the subtree rooted at node x
, where c
is a boolean representing whether the edge between node x
and its parent (if any) is selected or not.",
"dp[x][c] = max(sum(dp[y][cy]) + v(nums[x], sum(cy) + c))
\r\nwhere cy
is 0
or 1
. \r\nWhen sum(cy) + c
is odd, v(nums[x], sum(cy) + c) = nums[x] XOR k
. \r\nWhen sum(cy) + c
is even, v(nums[x], sum(cy) + c) = nums[x]
.",
"There’s also an easier solution - does the parity of the number of elements where nums[i] XOR k > nums[i]
help?"
],
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