Create program.c

Graph Algorithms/Graph_Reversal/program.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct {
+    int* data;      // Dynamic array to store elements
+    int size;       // Current size of the array
+    int capacity;   // Current allocated capacity
+} AdjList;
+
+typedef struct {
+    AdjList* arr;   // Array of AdjLists representing the graph
+    int size;       // Number of nodes in the graph
+} Graph;
+
+// Initialize an AdjList with a given capacity
+void initAdjList(AdjList* al, int initialCapacity) {
+    al->data = (int*)malloc(initialCapacity * sizeof(int));
+    al->size = 0;
+    al->capacity = initialCapacity;
+}
+
+// Adds a value to the AdjList, resizing only if necessary
+void pushBack(AdjList* al, int value) {
+    if (al->size == al->capacity) {
+        al->capacity = al->capacity == 0 ? 2 : al->capacity * 2;
+        al->data = (int*)realloc(al->data, al->capacity * sizeof(int));
+    }
+    al->data[al->size++] = value;
+}
+
+// Initialize a graph with a given size (number of nodes)
+void initGraph(Graph* g, int size) {
+    g->arr = (AdjList*)malloc(size * sizeof(AdjList));
+    g->size = size;
+    for (int i = 0; i < size; ++i) {
+        initAdjList(&g->arr[i], 2);  // Small initial capacity to reduce reallocations
+    }
+}
+
+// Transpose the graph by reversing edges
+Graph solve(Graph* graph) {
+    Graph ans;
+    initGraph(&ans, graph->size);
+
+    for (int i = 0; i < graph->size; ++i) {
+        for (int j = 0; j < graph->arr[i].size; ++j) {
+            int x = graph->arr[i].data[j];
+            pushBack(&ans.arr[x], i);  // Add node 'i' to the list of node 'x' in the transposed graph
+        }
+    }
+    return ans;
+}
+
+// Print the adjacency list of the graph
+void printGraph(Graph* g) {
+    for (int i = 0; i < g->size; ++i) {
+        printf("[ ");
+        for (int j = 0; j < g->arr[i].size; ++j) {
+            printf("%d ", g->arr[i].data[j]);
+        }
+        printf("]\n");
+    }
+}
+
+int main() {
+    Graph graph;
+    initGraph(&graph, 5);
+
+    // Building the adjacency list for the input graph
+    pushBack(&graph.arr[0], 1);
+    pushBack(&graph.arr[0], 2);
+    pushBack(&graph.arr[1], 4);
+    pushBack(&graph.arr[2], 4);
+    pushBack(&graph.arr[3], 1);
+    pushBack(&graph.arr[3], 2);
+    pushBack(&graph.arr[4], 3);
+
+    Graph result = solve(&graph);
+    printGraph(&result);
+    return 0;
+}