dijkstra

Author: okmd

graphs/lb-09-dijkstra.cpp

@@ -0,0 +1,55 @@
+int find_min(vector<int> &distance, int n, vector<int> &visited) {
+    int mn = INT_MAX;
+    int index = 0;
+    for (int i = 0; i < n; i++) {
+        if (!visited[i] and mn >= distance[i]) {
+            mn = distance[i];
+            index = i;
+        }
+    }
+    return index;
+}
+vector<int> dijkstra(int n, vector<vector<int>> adj[], int S) {
+    vector<int> distance(n, INT_MAX);
+    vector<int> visited(n, 0);
+
+    distance[S] = 0;
+    for (int i = 0; i < n - 1; i++) {
+        int min_dist_node = find_min(distance, n, visited);
+        visited[min_dist_node] = 1;
+        for (auto x : adj[min_dist_node]) {
+            int nei = x[0];
+            int dist = x[1];
+            if (!visited[nei] and distance[min_dist_node] != INT_MAX) {
+                distance[nei] = min(distance[nei], distance[min_dist_node] + dist);
+            }
+        }
+    }
+    return distance;
+}
+
+// QUEUE method
+
+vector<int> dijkstra(int n, vector<pair<int, int>> adj[], int src) {
+    // Array of vectors of pairs
+    // pair = (destination, cost)
+    // min-heap {dist, node}
+    priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> pq;
+    vector<int> distance(n + 1, INT_MAX);
+    distance[src] = 0;
+    pq.push({0, src});
+    while (pq.size()) {
+        int dist = pq.top().first;
+        int curr = pq.top().second;
+        pq.pop();
+        for (auto pr : adj[curr]) {
+            int neigh = pr.first;
+            int edge_cost = pr.second;
+            if (distance[neigh] > distance[curr] + edge_cost) {
+                distance[neigh] = distance[curr] + edge_cost;
+                pq.push({distance[neigh], neigh});
+            }
+        }
+    }
+    return distance;
+}