Dijkstra's Algorithm w/ Adjacency List Map c++

Question

Currently trying to implement dijkstra's algorithm in C++ by the use of an adjacency list in a text file read into a map object. The map is initialized as:

map<int, vector<pair<int, int>>> = adjList;

Sample text file input:

1 2,1 8,2
2 1,1 3,1
3 2,1 4,1
4 3,1 5,1
5 4,1 6,1
6 5,1 7,1
7 6,1 8,1
8 7,1 1,2

Where the key is a vertex, and the x values of the pairs in the vector are connected to the key vertex. The y values are the path distances. I pass that map into my dijkstra function, where I initialize a vector for shortest distances and a vector for storing visited vertices. My loop is where things start going wrong, as I get outputs of zeroes and very large numbers. Here's my code:

//checks if vertex has been visited or not
bool booler(int vertex, vector<int> visited){
    bool booly;
    if(find(visited.begin(), visited.end(), vertex) != visited.end()){
            booly = true;
        }
        else{
            booly = false;
        }
    return booly;
}
//checks vector for the shortest distance vertex
int minDist(vector<int> distances, vector<int> visited){
    int minDist = 1000000;
    int index;
    for(int v = 0; v < distances.size(); v++){
        if(booler(v, visited) == false && distances[v] < minDist){
            minDist = distances[v];
            index = v;
        }
    }
    return index;
}
void dijkstra(int source, map<int, vector<pair<int, int>>> adjList, int vSize){
    vector<int> distances(vSize, 1000000);
    vector<int> visited = {};
    distances[source] = 0;

    for(int c = 0; c < distances.size(); c++){
        int u = minDist(distances, visited);
        visited.push_back(u);
        for(int v = 1; v < distances.size(); v++){
            for(int s = 0; s < adjList[u].size(); s++){
                //updates distances based on v connection to u
                if(booler(v, visited) == false && distances[u] < 1000000 && adjList[u][s].second + distances[u] < distances[v]){
                    distances[v] = distances[u] + adjList[u][v].second;
                }
            }
        }
    }
    //prints out shortest path
    for(int x = 0; x < distances.size(); x++){
        cout << distances[x] << " " << endl;
    }

}

I haven't been able to fix this error, any help would be greatly appreciated!

Answer 1

Here is an implement how to use dijkstra.

https://www.quora.com/What-is-the-most-simple-efficient-C++-code-for-Dijkstras-shortest-path-algorithm

It is my solution for your problem:

#include "bits/stdc++.h"

using namespace std;

map<int, vector<pair<int, int> > > mp;

void addEdge(int u, int v, int dist) {
    mp[u].push_back(make_pair(v, dist));
}

void startDijkstra(int u) {
    vector<int> dist(1e2 + 1, 1e9);

    set<pair<int, int> > st;
    st.insert(make_pair(0, u));
    dist[u] = 0;

    while (!st.empty()) {
        pair<int, int> now = *st.begin();
        st.erase(st.begin());

        int v = now.second;
        int w = now.first;

        const vector<pair<int, int> > &edges = mp[v];
        for (const pair<int, int> &to : edges) {
            if (w + to.second < dist[to.first]) {
                st.erase(make_pair(dist[to.first], to.first));
                dist[to.first] = w + to.second;
                st.insert(make_pair(dist[to.first], to.first));
            }
        }
    }

    for (int i = 1; i <= 8; i++) {
        cout << i << ' ' << dist[i] << endl;
    }
}

int main() {
    addEdge(1, 2, 1);
    addEdge(1, 8, 2);

    addEdge(2, 1, 1);
    addEdge(2, 3, 1);

    addEdge(3, 2, 1);
    addEdge(3, 4, 1);

    addEdge(4, 3, 1);
    addEdge(4, 5, 1);

    addEdge(5, 4, 1);
    addEdge(5, 6, 1);

    addEdge(6, 5, 1);
    addEdge(6, 7, 1);

    addEdge(7, 6, 1);
    addEdge(7, 8, 1);

    addEdge(8, 9, 1);
    addEdge(8, 1, 2);

    startDijkstra(1);

    return 0;
}