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743. Network Delay Time.cpp
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743. Network Delay Time.cpp
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//🎯DAY 82 PROBLEM 1
/*We have to find the maximum time after which all the nodes should have got light from k, i.e. maximum shortest distance from the source to all the nodes
. So, we apply djikstra here to find the shortest path length from source to all the nodes & then find maximum among them.
*/
class Solution {
public:
int networkDelayTime(vector<vector<int>>& times, int n, int k) {
vector<pair<int,int>>adj[n+1];
for(int i=0;i<times.size();i++)
{
int src=times[i][0];
int des=times[i][1];
int weight=times[i][2];
adj[src].push_back({des,weight});
}
priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>>min_heap;
vector<int>dis(n+1,INT_MAX);
int ans=-1;
dis[k]=0;/*distance from source to source is 0, so we need to set it 0 before going through all the other nodes.e*/
min_heap.push({0,k});
while(!min_heap.empty())
{
auto tp=min_heap.top();
int prev_node=tp.second;
min_heap.pop();
for(auto it:adj[prev_node])
{
int next_node=it.first;
int wt=it.second;
if(dis[prev_node]+wt<dis[next_node])
{
dis[next_node]=dis[prev_node]+wt;
min_heap.push({dis[next_node],next_node});
}
}
}
ans= *max_element(dis.begin()+1,dis.end());
return ans==INT_MAX?-1:ans; /*if the answer is INT_MAX , that means it is not possible to reach all nodes from k so we return -1*/
}
};