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2242. Maximum Score of a Node Sequence 👍

  • Time: $O(|V| + |E|)$
  • Space: $O(|V| + |E|)$
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class Solution {
 public:
  int maximumScore(vector<int>& scores, vector<vector<int>>& edges) {
    int ans = -1;
    vector<set<pair<int, int>>> graph(scores.size());  // {(score, node)}

    for (const vector<int>& edge : edges) {
      const int u = edge[0];
      const int v = edge[1];
      graph[u].emplace(scores[v], v);
      graph[v].emplace(scores[u], u);
      if (graph[u].size() > 3)
        graph[u].erase(graph[u].begin());
      if (graph[v].size() > 3)
        graph[v].erase(graph[v].begin());
    }

    // Target sequence: a - u - v - b
    // Enumerate each edge (u, v), and find a (u's child) and b (v's child)
    // that's why we find the 3 children that have the highest scores because
    // One of the 3 children is guaranteed to be valid
    for (const vector<int>& edge : edges) {
      const int u = edge[0];
      const int v = edge[1];
      for (const auto& [scoreA, a] : graph[u])
        for (const auto& [scoreB, b] : graph[v])
          if (a != b && a != v && b != u)
            ans = max(ans, scoreA + scores[u] + scores[v] + scoreB);
    }

    return ans;
  }
};

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class Solution {
  public int maximumScore(int[] scores, int[][] edges) {
    final int n = scores.length;
    int ans = -1;
    Queue<Integer>[] graph = new Queue[n];

    for (int i = 0; i < n; ++i)
      graph[i] = new PriorityQueue<>((a, b) -> scores[a] - scores[b]);

    for (int[] edge : edges) {
      final int u = edge[0];
      final int v = edge[1];
      graph[u].offer(v);
      graph[v].offer(u);
      if (graph[u].size() > 3)
        graph[u].poll();
      if (graph[v].size() > 3)
        graph[v].poll();
    }

    // Target sequence: a - u - v - b
    // Enumerate each edge (u, v), and find a (u's child) and b (v's child)
    // that's why we find the 3 children that have the highest scores because
    // The third child is guaranteed to be a valid child
    for (int[] edge : edges) {
      final int u = edge[0];
      final int v = edge[1];
      for (final int a : graph[u])
        for (final int b : graph[v])
          if (a != b && a != v && b != u)
            ans = Math.max(ans, scores[a] + scores[u] + scores[v] + scores[b]);
    }

    return ans;
  }
}

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class Solution:
  def maximumScore(self, scores: List[int], edges: List[List[int]]) -> int:
    n = len(scores)
    ans = -1
    graph = [[] for _ in range(n)]

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

    for i in range(n):
      graph[i] = heapq.nlargest(3, graph[i])

    for u, v in edges:
      for scoreA, a in graph[u]:
        for scoreB, b in graph[v]:
          if a != b and a != v and b != u:
            ans = max(ans, scoreA + scores[u] + scores[v] + scoreB)

    return ans