Minimum time required to visit all the special nodes of a Tree

Given an undirected tree consisting of N vertices where some of the nodes are special nodes, the task is to visit all the special nodes from the root node in minimum time. Time for travelling from one node to another node can be assumed as unit time.

A node is special if the path from the root to the node consists of distinct value nodes.

Input: N = 7, edges[] = {(0, 1), (0, 2), (1, 4), (1, 5), (2, 3), (2, 6)}
isSpecial[] = {false, false, true, false, true, true, false}
Output: 8
Explanation:


Input: N = 7, edges[] = {(0, 1), (0, 2), (1, 4), (1, 5), (2, 3), (2, 6)}
isSpecial[] = {false, false, true, false, false, true, false}
Output: 6
Explanation:

Approach: The idea is to use Depth First Search traversal and traverse the nodes. If any node is having a children which is a special node, add two to the steps required for that node. Also mark that node as a special node such that while moving up the steps are taken into consideration.

Below is the implementation of the above approach:

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// C++ implementation to find
// the minimum time required to
// visit special nodes of a tree
  
#include <bits/stdc++.h>
using namespace std;
  
const int N = 100005;
  
// Time required to collect
vector<int> ans(N, 0);
  
vector<int> flag(N, 0);
  
// Minimum time required to reach
// all the special nodes of tree
void minimumTime(int u, int par,
                 vector<bool>& hasApple,
                 vector<int> adj[])
{
  
    // Condition to check if
    // the vertex has apple
    if (hasApple[u] == true)
        flag[u] = 1;
  
    // Iterate all the
    // adjacent of vertex u.
    for (auto it : adj[u]) {
  
        // if adjacent vertex
        // is it's parent
        if (it != par) {
            minimumTime(it, u, hasApple, adj);
  
            // if any vertex of subtree
            // it contain apple
            if (flag[it] > 0)
                ans[u] += (ans[it] + 2);
  
            // flagbit for node u
            // would be on if any vertex
            // in it's subtree contain apple
            flag[u] |= flag[it];
        }
    }
}
  
// Driver Code
int main()
{
    // Number of the vertex.
    int n = 7;
  
    vector<bool> hasApple{ false, false,
                           true, false,
                           true, true,
                           false };
  
    // Store all the edges,
    // any edge represented
    // by pair of vertex
    vector<pair<int, int> > edges;
  
    // Added all the
    // edge in edges vector.
    edges.push_back(make_pair(0, 1));
    edges.push_back(make_pair(0, 2));
    edges.push_back(make_pair(1, 4));
    edges.push_back(make_pair(1, 5));
    edges.push_back(make_pair(2, 3));
    edges.push_back(make_pair(2, 6));
  
    // Adjacent list
    vector<int> adj[n];
  
    for (int i = 0; i < edges.size(); i++) {
        int source_node = edges[i].first;
  
        int destination_node
            = edges[i].second;
  
        adj[source_node]
            .push_back(destination_node);
  
        adj[destination_node]
            .push_back(source_node);
    }
  
    // Function Call
    minimumTime(0, -1, hasApple, adj);
  
    cout << ans[0];
    return 0;
}
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Output:
8

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