HackerEarth Water supply problem solution

YASH PAL, 31 July 202416 February 2026

In this HackerEarth Water supply problem solution Your country can be represented by N cities connected using N – 1 roads. There exists an edge between city (i, i + 1) for all i from 1 to n – 1.

You have to set up a connection for water supply. You set this in one city and water gets transported from it to other cities using road transport. Certain cities are blocked which means that water cannot pass through this city. Determine the maximum number of cities to which water can be supplied.

HackerEarth Water supply problem solution

HackerEarth Water supply problem solution.

#include<bits/stdc++.h>
#define ll long long int
using namespace std;
vector<int>adjacent[200005];
bool visited[200005];
bool blocked[200005];
int sz;

void dfs(int u)
{
    visited[u] = true;
    sz++;
    for(int i = 0 ; i < adjacent[u].size() ; i++)
    {
        int v = adjacent[u][i];
        if(!visited[v] && blocked[v] == 0)
        {
            dfs(v);
        }
        else if(blocked[v])
        {
            sz++;
        }
    }
}


int main(){
    int n;
    cin>>n;

    for(int i = 0 ; i < n - 1 ; i++)
    {
        int u,v;
        cin>>u>>v;
        adjacent[u].push_back(v);
        adjacent[v].push_back(u);
    }

    for(int i = 1 ; i <= n ; i++)
    {
        int u;
        cin>>u;

        blocked[i] = u;
    }

    int ans = 1;
    for(int i = 1 ; i <= n ; i++)
    {
        if(visited[i] == false && blocked[i] == 0)
        {
            sz = 0;
            dfs(i);
            ans = max(ans,sz);
        }
    }

    cout<<ans<<endl;

}

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