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2440. Create Components With Same Value 👍

  • Time: $O(|\sqrt{\Sigma\texttt{nums[i]}}| \cdot n)$
  • Space: $O(n)$
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class Solution {
 public:
  int componentValue(vector<int>& nums, vector<vector<int>>& edges) {
    const int n = nums.size();
    const int sum = accumulate(nums.begin(), nums.end(), 0);
    vector<vector<int>> tree(n);

    for (const vector<int>& edge : edges) {
      const int u = edge[0];
      const int v = edge[1];
      tree[u].push_back(v);
      tree[v].push_back(u);
    }

    for (int i = n; i > 1; --i)
      // Split the tree into i parts, i.e. delete (i - 1) edges.
      if (sum % i == 0 && dfs(nums, tree, 0, sum / i, vector<bool>(n)) == 0)
        return i - 1;

    return 0;
  }

 private:
  static constexpr int kMax = 1'000'000'000;

  // Returns the sum of the subtree rooted at u substracting the sum of the
  // deleted subtrees.
  int dfs(const vector<int>& nums, const vector<vector<int>>& tree, int u,
          int target, vector<bool>&& seen) {
    int sum = nums[u];
    seen[u] = true;

    for (const int v : tree[u]) {
      if (seen[v])
        continue;
      sum += dfs(nums, tree, v, target, std::move(seen));
      if (sum > target)
        return kMax;
    }

    // Delete the tree that has sum == target.
    if (sum == target)
      return 0;
    return sum;
  }
};

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class Solution {
  public int componentValue(int[] nums, int[][] edges) {
    final int n = nums.length;
    final int sum = Arrays.stream(nums).sum();
    List<Integer>[] tree = new List[n];

    for (int i = 0; i < tree.length; ++i)
      tree[i] = new ArrayList<>();

    for (int[] edge : edges) {
      final int u = edge[0];
      final int v = edge[1];
      tree[u].add(v);
      tree[v].add(u);
    }

    for (int i = n; i > 1; --i)
      // Split the tree into i parts, i.e. delete (i - 1) edges.
      if (sum % i == 0 && dfs(nums, tree, 0, sum / i, new boolean[n]) == 0)
        return i - 1;

    return 0;
  }

  private static final int kMax = 1_000_000_000;

  // Returns the sum of the subtree rooted at u substracting the sum of the deleted subtrees.
  private int dfs(int[] nums, List<Integer>[] tree, int u, int target, boolean[] seen) {
    int sum = nums[u];
    seen[u] = true;

    for (final int v : tree[u]) {
      if (seen[v])
        continue;
      sum += dfs(nums, tree, v, target, seen);
      if (sum > target)
        return kMax;
    }

    // Delete the tree that has sum == target.
    if (sum == target)
      return 0;
    return sum;
  }
}

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class Solution:
  def componentValue(self, nums: list[int], edges: list[list[int]]) -> int:
    kMax = 1_000_000_000
    n = len(nums)
    summ = sum(nums)
    tree = [[] for _ in range(n)]

    for u, v in edges:
      tree[u].append(v)
      tree[v].append(u)

    def dfs(u: int, target: int, seen: set[bool]) -> int:
      """
      Returns the sum of the subtree rooted at u substracting the sum of the
      deleted subtrees.
      """
      summ = nums[u]
      seen.add(u)

      for v in tree[u]:
        if v in seen:
          continue
        summ += dfs(v, target, seen)
        if summ > target:
          return kMax

      # Delete the tree that has sum == target.
      if summ == target:
        return 0
      return summ

    for i in range(n, 1, -1):
      # Split the tree into i parts, i.e. delete (i - 1) edges.
      if summ % i == 0 and dfs(0, summ // i, set()) == 0:
        return i - 1

    return 0