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almostshortestpath.cpp
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almostshortestpath.cpp
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#include <vector>
#include <iostream>
#include <math.h>
using namespace std;
const int inf = 1 << 30;
// given adjacency matrix adj, finds shortest path from A to B
vector<int> dijk(int A, int B, vector< vector<int> > adj) {
int n = adj.size();
vector<int> dist(n);
vector<bool> vis(n);
vector<int> predecesors(n, -1);
for(int i = 0; i < n; ++i) {
dist[i] = inf;
}
dist[A] = 0;
for(int i = 0; i < n; ++i) {
int cur = -1;
for(int j = 0; j < n; ++j) {
if (vis[j]) continue;
if (cur == -1 || dist[j] < dist[cur]) {
cur = j;
}
}
vis[cur] = true;
for(int j = 0; j < n; ++j) {
int path = dist[cur] + adj[cur][j];
if (path < dist[j]) {
dist[j] = path;
predecesors[j] = cur;
}
}
}
// return dist[B];
return predecesors;
}
int main(){
ios::sync_with_stdio(false);
// cin.tie(NULL);
int points, routes, start, destination, x, y, weight;
cin >> points >> routes;
cin >> start >> destination;
vector< vector<int> > adj(points, vector<int>(points, 0));
for (int i = 0; i < routes; ++i){
cin >> x >> y;
cin >> weight;
adj[x][y] = weight;
}
vector<int> predecesors = dijk(start, destination, adj);
if(predecesors[destination] == -1){
cout << -1 << endl;
return 0;
}
//delete nodes of actual path
for (int i = 0; i < predecesors.size(); ++i)
{
if(predecesors[i] != -1)
adj[predecesors[i]][i] = inf;
}
predecesors = dijk(start, destination, adj);
if(predecesors[destination] == -1){
cout << -1 << endl;
return 0;
}
for (int i = 0; i < predecesors.size(); ++i)
{
cout << predecesors[i] << " " << endl;
}
int cost = 0;
int dest = destination;
while(dest != -1){
int pred = predecesors[dest];
printf("pred: %d, dest: %d, cost: %d\n", pred, dest, cost);
cout.flush();
cost += adj[pred][dest];
dest = pred;
}
cout << cost << endl;
return 0;
}