From bb36773be769d5aa52ea250223a86f1472c39355 Mon Sep 17 00:00:00 2001
From: jojbrasileiro <134644775+jojbrasileiro@users.noreply.github.com>
Date: Wed, 13 Nov 2024 21:38:13 -0300
Subject: [PATCH] Added A* algorithm

Added A* algorithm implementation to the repository.
---
 data_structures/graphs/a-star.c | 181 ++++++++++++++++++++++++++++++++
 1 file changed, 181 insertions(+)
 create mode 100644 data_structures/graphs/a-star.c

diff --git a/data_structures/graphs/a-star.c b/data_structures/graphs/a-star.c
new file mode 100644
index 0000000000..f9e179eeb8
--- /dev/null
+++ b/data_structures/graphs/a-star.c
@@ -0,0 +1,181 @@
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+// Structure for storing a graph
+struct Graph
+{
+    int vertexNum;
+    int **edges;
+};
+
+// Structure to represent a node in A*
+struct Node
+{
+    int f, g, h;
+    int parent;
+    bool is_in_closed_set;
+};
+
+// Creates a graph with V vertices
+void createGraph(struct Graph *G, int V)
+{
+    G->vertexNum = V;
+    G->edges = (int **)malloc(V * sizeof(int *));
+    for (int i = 0; i < V; i++)
+    {
+        G->edges[i] = (int *)malloc(V * sizeof(int));
+        for (int j = 0; j < V; j++) G->edges[i][j] = INT_MAX;
+        G->edges[i][i] = 0;
+    }
+}
+
+// Adds an edge to the graph with a specified weight
+void addEdge(struct Graph *G, int src, int dst, int weight)
+{
+    G->edges[src][dst] = weight;
+}
+
+// Heuristic function (Manhattan distance for simplicity)
+int heuristic(int start, int goal) { return abs(start - goal); }
+
+// Utility function to find the node with the lowest f in the open set
+int minFNode(int openSet[], struct Node nodes[], int openSetSize)
+{
+    int minF = INT_MAX;
+    int minNode = -1;
+    for (int i = 0; i < openSetSize; i++)
+    {
+        int node = openSet[i];
+        if (nodes[node].f < minF)
+        {
+            minF = nodes[node].f;
+            minNode = node;
+        }
+    }
+    return minNode;
+}
+
+// Function to reconstruct and print the path from start to goal
+void printPath(struct Node nodes[], int goal)
+{
+    if (nodes[goal].parent != -1)
+    {
+        printPath(nodes, nodes[goal].parent);
+    }
+    printf("%d ", goal);
+}
+
+// A* Algorithm function
+void aStar(struct Graph *graph, int start, int goal)
+{
+    int V = graph->vertexNum;
+    struct Node nodes[V];
+    int openSet[V];
+    int openSetSize = 0;
+
+    // Initialize nodes and add start to open set
+    for (int i = 0; i < V; i++)
+    {
+        nodes[i].f = nodes[i].g = nodes[i].h = INT_MAX;
+        nodes[i].parent = -1;
+        nodes[i].is_in_closed_set = false;
+    }
+    nodes[start].g = 0;
+    nodes[start].h = heuristic(start, goal);
+    nodes[start].f = nodes[start].g + nodes[start].h;
+    openSet[openSetSize++] = start;
+
+    // Main A* loop
+    while (openSetSize > 0)
+    {
+        int current = minFNode(openSet, nodes, openSetSize);
+
+        // If goal is reached, reconstruct path
+        if (current == goal)
+        {
+            printf("Path from %d to %d: ", start, goal);
+            printPath(nodes, goal);
+            printf("\n");
+            return;
+        }
+
+        // Remove current from open set
+        int index = 0;
+        while (index < openSetSize && openSet[index] != current) index++;
+        for (int i = index; i < openSetSize - 1; i++)
+            openSet[i] = openSet[i + 1];
+        openSetSize--;
+
+        nodes[current].is_in_closed_set = true;
+
+        // Check neighbors
+        for (int neighbor = 0; neighbor < V; neighbor++)
+        {
+            if (graph->edges[current][neighbor] != INT_MAX &&
+                !nodes[neighbor].is_in_closed_set)
+            {
+                int tentative_g =
+                    nodes[current].g + graph->edges[current][neighbor];
+
+                if (tentative_g < nodes[neighbor].g)
+                {
+                    nodes[neighbor].parent = current;
+                    nodes[neighbor].g = tentative_g;
+                    nodes[neighbor].h = heuristic(neighbor, goal);
+                    nodes[neighbor].f = nodes[neighbor].g + nodes[neighbor].h;
+
+                    // Add neighbor to open set if not already present
+                    bool inOpenSet = false;
+                    for (int i = 0; i < openSetSize; i++)
+                    {
+                        if (openSet[i] == neighbor)
+                        {
+                            inOpenSet = true;
+                            break;
+                        }
+                    }
+                    if (!inOpenSet)
+                        openSet[openSetSize++] = neighbor;
+                }
+            }
+        }
+    }
+
+    printf("No path found from %d to %d\n", start, goal);
+}
+
+// Driver function
+int main()
+{
+    int V, E;
+    int src, dst, weight;
+    struct Graph G;
+    printf("Enter number of vertices: ");
+    scanf("%d", &V);
+    printf("Enter number of edges: ");
+    scanf("%d", &E);
+    createGraph(&G, V);
+
+    for (int i = 0; i < E; i++)
+    {
+        printf("\nEdge %d \nEnter source: ", i + 1);
+        scanf("%d", &src);
+        printf("Enter destination: ");
+        scanf("%d", &dst);
+        printf("Enter weight: ");
+        scanf("%d", &weight);
+        addEdge(&G, src, dst, weight);
+    }
+
+    int start, goal;
+    printf("\nEnter start node: ");
+    scanf("%d", &start);
+    printf("Enter goal node: ");
+    scanf("%d", &goal);
+
+    aStar(&G, start, goal);
+
+    return 0;
+}