Most Profitable Path in a Tree

Updated on 19 June, 2025
Most Profitable Path in a Tree header image

Problem Statement

In a game played on an undirected tree consisting of n nodes labeled from 0 to n - 1 and rooted at node 0, we are given a list of edges connecting these nodes, defining the structure of the tree. Each node on this tree has a gate associated with it, and each gate either has a cost to open (if the value is negative) or offers a reward (if the value is positive).

Alice begins the game at the root node (node 0), and Bob starts at a given node (bob). As the game progresses, both move to adjacent nodes at the same time intervals—Alice aiming for a leaf node, and Bob heading back to the root. Costs and rewards at each gate they pass are settled depending on whether they cross it alone or together. Should they reach their respective destinations, their movement ceases. Our objective is to calculate the maximum potential net income Alice could collect by choosing an optimal path toward any leaf node.

Examples

Example 1

Input:

edges = [[0,1],[1,2],[1,3],[3,4]], bob = 3, amount = [-2,4,2,-4,6]

Output:

6

Explanation:

The above diagram represents the given tree. The game goes as follows:
- Alice is initially on node 0, Bob on node 3. They open the gates of their respective nodes.
Alice's net income is now -2.
- Both Alice and Bob move to node 1.
  Since they reach here simultaneously, they open the gate together and share the reward.
  Alice's net income becomes -2 + (4 / 2) = 0.
- Alice moves on to node 3. Since Bob already opened its gate, Alice's income remains unchanged.
  Bob moves on to node 0, and stops moving.
- Alice moves on to node 4 and opens the gate there. Her net income becomes 0 + 6 = 6.
Now, neither Alice nor Bob can make any further moves, and the game ends.
It is not possible for Alice to get a higher net income.

Example 2

Input:

edges = [[0,1]], bob = 1, amount = [-7280,2350]

Output:

-7280

Explanation:

Alice follows the path 0->1 whereas Bob follows the path 1->0.
Thus, Alice opens the gate at node 0 only. Hence, her net income is -7280.

Constraints

  • 2 <= n <= 105
  • edges.length == n - 1
  • edges[i].length == 2
  • 0 <= ai, bi < n
  • ai != bi
  • edges represents a valid tree.
  • 1 <= bob < n
  • amount.length == n
  • amount[i] is an even integer in the range [-104, 104].

Approach and Intuition

Considering the movement of Alice and Bob and the interaction at each gate, the approach to solve this requires several important considerations:

  1. Path Tracking:

    • Since the tree is undirected and rooted, we can use depth-first search (DFS) to track paths from node 0 to all possible leaf nodes.
    • For Bob's movement from node bob to node 0, we'll track the path using a backtracking method or BFS since his start and end point are predefined.
  2. Joint Movements:

    • Calculate the series of nodes at which both Alice and Bob will be present simultaneously. This can be derived from the intersection of Alice's path towards any leaf and Bob's path towards the root node.
  3. Cost and Reward Calculation:

    • For each node visited solely by Alice or Bob, add or subtract the full amount to/from Alice’s running income based on whether it’s a reward or a fee.
    • For nodes where both Alice and Bob are present together, they share the fee or reward, so add/subtract half the amount from Alice's income.
  4. Maximizing Income:

    • For each leaf node in the tree, simulate the entire sequence of moves for Alice while considering Bob’s movements toward the root.
    • Keep updating the maximum net income Alice could achieve on reaching each leaf node.
    • Return the maximum of these incomes as the result, ensuring the solution caters efficiently to scenarios where Alice and Bob may meet multiple times or do not meet at all.

This systematic breakdown respects the constraints and manages the computation within efficient boundaries, particularly considering the limit on the number of nodes and potential paths Alice and Bob can take.

Solutions

  • C++
  • Java
  • Python
cpp
class ProfitablePathCalc {
public:
    int optimalPathProfit(vector<vector<int>>& connections, int bobLoc,
                          vector<int>& profits) {
        nodeCount = profits.size();
        adjacencyList.resize(nodeCount, vector<int>());

        // Building the adjacency list
        for (vector<int> connection : connections) {
            adjacencyList[connection[0]].push_back(connection[1]);
            adjacencyList[connection[1]].push_back(connection[0]);
        }
        bobDistance.resize(nodeCount);
        return calculateProfit(0, -1, 0, bobLoc, profits);
    }

private:
    vector<vector<int>> adjacencyList;
    vector<int> bobDistance;
    int nodeCount;

    // DFS to determine maximum potential profit
    int calculateProfit(int node, int parent, int duration, int bobLoc,
                        vector<int>& profits) {
        int maximumProfit = 0, highestChildProfit = INT_MIN;

        // Setting nodes' distances relative to Bob's location
        if (node == bobLoc)
            bobDistance[node] = 0;
        else
            bobDistance[node] = nodeCount;
        for (int neighbor : adjacencyList[node]) {
            if (neighbor != parent) {
                highestChildProfit = max(highestChildProfit, calculateProfit(neighbor, node,
                                                    duration + 1, bobLoc, profits));
                bobDistance[node] =
                    min(bobDistance[node],
                        bobDistance[neighbor] + 1);
            }
        }
        // Check if only Alice (not Bob) has reached the node
        if (bobDistance[node] > duration) maximumProfit += profits[node];

        // Check if both Alice and Bob reach the node simultaneously
        else if (bobDistance[node] == duration)
            maximumProfit += profits[node] / 2;

        // Include child node profits for the total profit
        if (highestChildProfit == INT_MIN)
            return maximumProfit;
        else
            return maximumProfit + highestChildProfit;
    }
};

The provided C++ code defines a class ProfitablePathCalc that calculates the most profitable path in a tree where nodes represent locations with certain profits, and Alice and Bob traverse the tree starting from different nodes. Here’s how the solution works:

  • The primary public method optimalPathProfit accepts the connections representing the tree edges, the starting location of Bob (bobLoc), and a list representing the profit at each node (profits).
  • The method constructs an adjacency list for the tree and initializes Bob's distances from each node to an array.
  • It invokes a private helper method calculateProfit to determine the maximum profit Alice can accumulate starting from the root node under certain conditions regarding her and Bob's simultaneous node visits.

Steps for calculating the maximum profit:

  1. Construct the tree using an adjacency list, where each node can access its direct neighbors.
  2. Perform a depth-first search (DFS) through the tree starting from the root node. During this search:
    • Update the shortest distance from Bob's current location to other nodes.
    • Calculate the potential profit if Alice reaches a node either alone or at the same time as Bob.
      • If Alice reaches a node alone (before Bob), she collects the full profit of the node.
      • If both reach the node simultaneously, profits are shared, and each gets half.
  • The DFS helps propagate the distance from Bob and potential profits up the tree, combining the profits of child nodes with the current node's profit based on the visiting conditions.
  • The final result is the maximum profit Alice can gather from the tree.

This code efficiently uses graph traversal and dynamic programming techniques to solve the problem of finding the most profitable path in a tree structured data with specific traversal rules.

java
class Solution {

    public int maximumProfitFromPath(int[][] connections, int bobLocation, int[] profits) {
        int verticesCount = profits.length;
        var graph = new ArrayList<ArrayList<Integer>>();
        for (int i = 0; i < verticesCount; i++) {
            graph.add(new ArrayList<>());
        }
        int[] distances = new int[verticesCount];

        // Construct the graph from connections
        for (int[] connection : connections) {
            graph.get(connection[0]).add(connection[1]);
            graph.get(connection[1]).add(connection[0]);
        }

        return calculateMaxProfit(0, 0, 0, bobLocation, profits);
    }

    private ArrayList<ArrayList<Integer>> graph;
    private int[] distances;
    private int totalVertices;

    // Recursive DFS function to compute the profit
    private int calculateMaxProfit(
        int currentNode,
        int parent,
        int currentTime,
        int bobLocation,
        int[] profits
    ) {
        int bestProfit = 0, maxSubtreeProfit = Integer.MIN_VALUE;

        // Initialize distances from Bob's location
        if (currentNode == bobLocation) {
            distances[currentNode] = 0;
        } else {
            distances[currentNode] = totalVertices;
        }

        for (int neighbor : graph.get(currentNode)) {
            if (neighbor != parent) {
                int childProfit = calculateMaxProfit(neighbor, currentNode, currentTime + 1, bobLocation, profits);
                maxSubtreeProfit = Math.max(maxSubtreeProfit, childProfit);
                distances[currentNode] = Math.min(distances[currentNode], distances[neighbor] + 1);
            }
        }

        // Condition when Alice gets to the node first
        if (distances[currentNode] > currentTime) {
            bestProfit += profits[currentNode];
        }
        // Condition when both reach at the same time
        else if (distances[currentNode] == currentTime) {
            bestProfit += profits[currentNode] / 2;
        }

        // Determine the profit to return, considering child nodes
        return (maxSubtreeProfit == Integer.MIN_VALUE) ? bestProfit : bestProfit + maxSubtreeProfit;
    }
}

The Java solution for the "Most Profitable Path in a Tree" problem involves creating a method to determine the maximum profit possible as one moves through the tree. Here's how it operates:

  • The class Solution contains the method maximumProfitFromPath which initializes a graph from the given connections and utilizes a recursive depth-first search (DFS) method calculateMaxProfit to compute the profit.
  • The graph is represented as an adjacency list, and each node corresponds to a profit value stored in the profits array.
  • During graph construction, for each connection, ensure bidirectional continuity by adding the nodes to each others' adjacency list.

The recursive calculateMaxProfit function performs the following:

  • Uses DFS to traverse the tree from a given starting node.
  • Each node keeps track of the profit collected, considering different conditions:
    • If reached before Bob, Alice collects all the profits of that node.
    • If both Alice and Bob reach the node simultaneously, profits are shared equally.
  • The recursion maintains a count of current time (depth in recursion acts like time elapsed) and distance from Bob for each node.
  • After visiting all neighbors of a node, it decides the maximum profit from that node:
    • If no profit from sub-nodes, takes current node's profit.
    • Otherwise, aggregates the current node's and maximum of child nodes' profit.

This design utilizes depth-first traversal and recursive backtracking to evaluate different paths and their respective profits, ensuring the optimization of return on the basis of conditions met at each node while managing both current and path-relative computations effectively.

python
class ProfitCalculator:
    def __init__(self):
        self.graph = []
        self.bob_dist = []
        self.total_nodes = 0

    def optimalPathValue(self, connections, bob_location, profits):
        self.total_nodes = len(profits)
        self.graph = [[] for _ in range(self.total_nodes)]
        self.bob_dist = [0] * self.total_nodes

        # Establish graph with connections
        for conn in connections:
            self.graph[conn[0]].append(conn[1])
            self.graph[conn[1]].append(conn[0])

        return self.calculateProfit(0, 0, 0, bob_location, profits)

    # Perform Depth-first Search
    def calculateProfit(self, node, parent, steps, bob_location, profits):
        highest_profit = 0
        deepest_profit = float("-inf")

        # Set distance from Bob
        if node == bob_location:
            self.bob_dist[node] = 0
        else:
            self.bob_dist[node] = self.total_nodes

        for neighbor in self.graph[node]:
            if neighbor != parent:
                deepest_profit = max(
                    deepest_profit,
                    self.calculateProfit(neighbor, node, steps + 1, bob_location, profits),
                )
                self.bob_dist[node] = min(
                    self.bob_dist[node],
                    self.bob_dist[neighbor] + 1,
                )

        # Consider profits depending on reach times
        if self.bob_dist[node] > steps:
            highest_profit += profits[node]
        elif self.bob_dist[node] == steps:
            highest_profit += profits[node] // 2

        # Collect total profits including children nodes
        return highest_profit if deepest_profit == float("-inf") else highest_profit + deepest_profit

The Python program provided models a profit calculation scenario on a tree-like structure using a depth-first search (DFS) approach. It determines a path through nodes, maximizing profits while considering distances relevant to a specific starting node (referred to as Bob's location).

  • Begin by initializing the ProfitCalculator class to manage the tree graph and distances from Bob's location, along with maintaining a total count of nodes.
  • The optimalPathValue function sets up a directed adjacency list for the node connections and initializes distance metrics.
  • For each connection, both directions are noted, creating an undirected graph effectively, and an adjacency list is constructed.
  • The critical function, calculateProfit, is recursively called to navigate the tree, beginning at the root. This function carries out numerous checks and calculations:
    • It initializes the distance from Bob's location and ensures each node only notes the shortest distance from Bob.
    • For each child node (or connected neighbor), it calculates profits recursively and determines total profits by comparing depths and distances to Bob's location.

The decision-making integrates checking paths accessible within certain steps compared to the distance from Bob's location. If a node is further from Bob than the steps taken to reach it, the node's profit is added fully. If the node is reached exactly at the same step count as its distance from Bob, half of the node's profit is considered.

The algorithm effectively merges integer-based profit handling within tree traversal, showcasing a tailored solution that prioritizes path profitability based on specific distance criteria, making it an efficient solution for problems involving spatial relationships and path profitability in trees.

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