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Reverse Min egdes in graph.cpp
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Reverse Min egdes in graph.cpp
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#include<iostream>
#include<cstdio>
#include<list>
#include<climits>
using namespace std;
/* Given a directed graph with vertice V ( from 1 to N ) and
Edges E , the following program calcualtes the min no of edges to be reversed to establish
a path from vertex 1 to N */
class Graph{
int V,E;
list<int> *SAdj;
list<int> *RAdj;
public:
Graph(int V,int E);
void addSEdge(int u,int v);
void addREdge(int u,int v);
int calcMinEdges(int s);
};
Graph::Graph(int V,int E){
this->V = V;
this->E = E;
SAdj = new list<int>[V+1];
RAdj = new list<int>[V+1];
}
void Graph::addSEdge(int u,int v){
SAdj[u].push_back(v);
}
void Graph::addREdge(int u,int v){
RAdj[u].push_back(v);
}
int Graph::calcMinEdges(int s){
int dist[V+1];
for(int i=2;i<=V;i++)
dist[V]=INT_MAX;
list<int> q;
dist[s]=0;
q.push_back(s);
list<int>::iterator i,j;
while(!q.empty()){
int s = q.front();
q.pop_front();
for(i=SAdj[s].begin();i!=SAdj[s].end();i++){
if(dist[*i]>dist[s])
{ dist[*i]=dist[s];
q.push_back(*i);
}
}
for(j=RAdj[s].begin();j!=RAdj[s].end();j++){
if(dist[*j]>dist[s]+1)
{ dist[*j]=dist[s]+1;
q.push_back(*j);
}
}
}
if(dist[V]==INT_MAX)
return -1;
else
return dist[V];
}
int main(){
int V,E;
int u,v;
scanf("%d%d",&V,&E);
Graph g(V,E);
for(int i=0;i<E;i++){
scanf("%d%d",&u,&v);
g.addSEdge(u,v);
g.addREdge(v,u);
}
printf("%d\n",g.calcMinEdges(1));
return 0;
}