progress

CMakeLists.txt

@@ -9,6 +9,9 @@ add_executable(graphe main.c
         structs.c
         structs.h
         render.h
-        render.c)
+        render.c
+        algorithms.h
+        communities.c
+        louvain.c)
 
 target_link_libraries(graphe SDL2::SDL2 m)

algorithms.h

@@ -0,0 +1,48 @@
+//
+// Created by Tiago Batista Cardoso on 2/26/2026.
+//
+
+#ifndef GRAPHE_ALGORITHMS_H
+#define GRAPHE_ALGORITHMS_H
+
+#include "structs.h"
+
+// -- k-clique communities
+struct community_t {
+	int *members; // node ids in this community
+	int size;
+};
+typedef struct community_t community_t;
+
+struct community_result_t {
+	community_t *communities;
+	int count;
+	int *node_community; // node_community[i] = community index of node i (-1 if none)
+};
+typedef struct community_result_t community_result_t;
+
+community_result_t *find_k_clique_communities(const graph_t *graph, int k);
+void free_community_result(community_result_t *result);
+
+// -- louvain
+struct louvain_result_t {
+	int *node_community; // node_community[i] = community id of node i
+	int count; // total number of communities
+	double modularity; // final modularity score
+};
+typedef struct louvain_result_t louvain_result_t;
+
+louvain_result_t *compute_louvain(const graph_t *graph);
+void free_louvain_result(louvain_result_t *result);
+
+// -- hybrid algorithm
+struct hybrid_result_t {
+	int *node_community; // node_community[i] = community id of node i
+	int count; // total number of communities
+};
+typedef struct hybrid_result_t hybrid_result_t;
+
+hybrid_result_t *hybrid_community_detection(const graph_t *graph, int k);
+void free_hybrid_result(hybrid_result_t *result);
+
+#endif

communities.c

@@ -0,0 +1,166 @@
+//
+// Created by Tiago Batista Cardoso on 2/26/2026.
+//
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "algorithms.h"
+
+static int has_edge(const graph_t *graph, int u, int v)
+{
+	node_t *n = graph->adj_lists[u];
+	while (n) {
+		if (n->id == v)
+			return 1;
+		n = n->next;
+	}
+	return 0;
+}
+
+typedef struct {
+	int **list;
+	int count;
+	int capacity;
+	int k;
+} clique_store_t;
+
+static void store_clique(clique_store_t *store, int *current)
+{
+	if (store->count >= store->capacity) {
+		store->capacity *= 2;
+		store->list =
+			realloc(store->list, store->capacity * sizeof(int *));
+	}
+	int *copy = malloc(store->k * sizeof(int));
+	memcpy(copy, current, store->k * sizeof(int));
+	store->list[store->count++] = copy;
+}
+
+static void enumerate_cliques(const graph_t *graph, clique_store_t *store,
+			      int *current, int depth, int start)
+{
+	if (depth == store->k) {
+		store_clique(store, current);
+		return;
+	}
+	for (int v = start; v < graph->n; v++) {
+		// v must be connected to all nodes already in current
+		int ok = 1;
+		for (int i = 0; i < depth; i++) {
+			if (!has_edge(graph, current[i], v)) {
+				ok = 0;
+				break;
+			}
+		}
+		if (!ok)
+			continue;
+		current[depth] = v;
+		enumerate_cliques(graph, store, current, depth + 1, v + 1);
+	}
+}
+
+static int uf_find(int *parent, int x)
+{
+	while (parent[x] != x) {
+		parent[x] = parent[parent[x]];
+		x = parent[x];
+	}
+	return x;
+}
+
+static void uf_union(int *parent, int *rank, int a, int b)
+{
+	a = uf_find(parent, a);
+	b = uf_find(parent, b);
+	if (a == b)
+		return;
+	if (rank[a] < rank[b]) {
+		int t = a;
+		a = b;
+		b = t;
+	}
+	parent[b] = a;
+	if (rank[a] == rank[b])
+		rank[a]++;
+}
+
+community_result_t *find_k_clique_communities(const graph_t *graph, int k)
+{
+	int n = graph->n;
+
+	// find all k-cliques
+	clique_store_t store = { .list = malloc(64 * sizeof(int *)),
+				 .count = 0,
+				 .capacity = 64,
+				 .k = k };
+	int *current = malloc(k * sizeof(int));
+	enumerate_cliques(graph, &store, current, 0, 0);
+	free(current);
+
+	printf("[communities] found %d %d-cliques\n", store.count, k);
+
+	int *parent = malloc(store.count * sizeof(int));
+	int *rank = calloc(store.count, sizeof(int));
+	for (int i = 0; i < store.count; i++)
+		parent[i] = i;
+
+	for (int i = 0; i < store.count; i++) {
+		for (int j = i + 1; j < store.count; j++) {
+			// Count shared nodes
+			int shared = 0;
+			for (int a = 0; a < k; a++)
+				for (int b = 0; b < k; b++)
+					if (store.list[i][a] ==
+					    store.list[j][b])
+						shared++;
+			if (shared >= k - 1)
+				uf_union(parent, rank, i, j);
+		}
+	}
+
+	community_result_t *result = malloc(sizeof(community_result_t));
+	result->node_community = malloc(n * sizeof(int));
+	for (int i = 0; i < n; i++)
+		result->node_community[i] = -1;
+
+	for (int i = 0; i < store.count; i++) {
+		int community_id = uf_find(parent, i);
+		for (int j = 0; j < k; j++) {
+			int node = store.list[i][j];
+			result->node_community[node] = community_id;
+		}
+	}
+
+	int *id_map = malloc(store.count * sizeof(int));
+	memset(id_map, -1, store.count * sizeof(int));
+	int next_id = 0;
+	for (int i = 0; i < n; i++) {
+		int c = result->node_community[i];
+		if (c == -1)
+			continue;
+		if (id_map[c] == -1)
+			id_map[c] = next_id++;
+		result->node_community[i] = id_map[c];
+	}
+	result->count = next_id;
+	printf("[communities] found %d communities\n", result->count);
+
+	// cleanup
+	for (int i = 0; i < store.count; i++)
+		free(store.list[i]);
+	free(store.list);
+	free(parent);
+	free(rank);
+	free(id_map);
+
+	return result;
+}
+
+void free_community_result(community_result_t *result)
+{
+	if (!result)
+		return;
+	free(result->node_community);
+	free(result);
+}

louvain.c

@@ -0,0 +1,215 @@
+//
+// Created by Tiago Batista Cardoso on 2/26/2026.
+//
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+#include "algorithms.h"
+
+// -- helper methods
+
+// total number of edges
+static int count_edges(const graph_t *graph)
+{
+	int count = 0;
+	for (int i = 0; i < graph->n; i++) {
+		node_t *n = graph->adj_lists[i];
+		while (n) {
+			count++;
+			n = n->next;
+		}
+	}
+	return count / 2; // undirected
+}
+
+// degree of node i
+static int degree(const graph_t *graph, int i)
+{
+	int d = 0;
+	node_t *n = graph->adj_lists[i];
+	while (n) {
+		d++;
+		n = n->next;
+	}
+	return d;
+}
+
+// sum of weights of edges from node i to community c
+static double k_i_in(const graph_t *graph, int i, int c, int *community)
+{
+	double sum = 0.0;
+	node_t *n = graph->adj_lists[i];
+	while (n) {
+		if (community[n->id] == c)
+			sum += 1.0;
+		n = n->next;
+	}
+	return sum;
+}
+
+// Sum of degrees of all nodes in community c
+static double sigma_tot(const graph_t *graph, int c, int *community)
+{
+	double sum = 0.0;
+	for (int i = 0; i < graph->n; i++)
+		if (community[i] == c)
+			sum += degree(graph, i);
+	return sum;
+}
+
+// ΔQ = [ (k_i_in - sigma_tot * k_i / 2m) / m ]
+static double delta_modularity(const graph_t *graph, int i, int c,
+			       int *community, double m)
+{
+	double ki = degree(graph, i);
+	double ki_in = k_i_in(graph, i, c, community);
+	double sig = sigma_tot(graph, c, community);
+
+	return (ki_in - (sig * ki) / (2.0 * m)) / m;
+}
+
+static int phase1(const graph_t *graph, int *community, double m)
+{
+	int n = graph->n;
+	int improved = 1;
+	int total_moves = 0;
+
+	while (improved) {
+		improved = 0;
+		for (int i = 0; i < n; i++) {
+			int best_community = community[i];
+			double best_gain = 0.0;
+
+			// Collect neighboring communities
+			int *neighbor_communities = calloc(n, sizeof(int));
+			int nc_count = 0;
+			node_t *nb = graph->adj_lists[i];
+			while (nb) {
+				int c = community[nb->id];
+				// Check if already in list
+				int found = 0;
+				for (int x = 0; x < nc_count; x++)
+					if (neighbor_communities[x] == c) {
+						found = 1;
+						break;
+					}
+				if (!found)
+					neighbor_communities[nc_count++] = c;
+				nb = nb->next;
+			}
+
+			// temporarily remove i from its community
+			int old_community = community[i];
+			community[i] = -1;
+
+			// try moving i to each neighboring community
+			for (int x = 0; x < nc_count; x++) {
+				int c = neighbor_communities[x];
+				if (c == old_community)
+					continue;
+				double gain = delta_modularity(graph, i, c,
+							       community, m) -
+					      delta_modularity(graph, i,
+							       old_community,
+							       community, m);
+				if (gain > best_gain) {
+					best_gain = gain;
+					best_community = c;
+				}
+			}
+
+			community[i] = best_community;
+
+			if (best_community != old_community) {
+				improved = 1;
+				total_moves++;
+			}
+
+			free(neighbor_communities);
+		}
+	}
+
+	return total_moves;
+}
+
+static double compute_modularity(const graph_t *graph, int *community, double m)
+{
+	int n = graph->n;
+	double Q = 0.0;
+
+	for (int i = 0; i < n; i++) {
+		node_t *nb = graph->adj_lists[i];
+		while (nb) {
+			int j = nb->id;
+			if (community[i] == community[j])
+				Q += 1.0 - ((double)degree(graph, i) *
+					    degree(graph, j)) /
+						   (2.0 * m);
+			nb = nb->next;
+		}
+	}
+	return Q / (2.0 * m);
+}
+
+static int compact(int *community, int n)
+{
+	int *map = malloc(n * sizeof(int));
+	memset(map, -1, n * sizeof(int));
+	int next = 0;
+	for (int i = 0; i < n; i++) {
+		if (community[i] == -1)
+			continue;
+		if (map[community[i]] == -1)
+			map[community[i]] = next++;
+		community[i] = map[community[i]];
+	}
+	free(map);
+	return next;
+}
+
+louvain_result_t *compute_louvain(const graph_t *graph)
+{
+	int n = graph->n;
+	double m = (double)count_edges(graph);
+
+	if (m == 0) {
+		printf("[louvain] no edges found\n");
+		louvain_result_t *r = malloc(sizeof(louvain_result_t));
+		r->node_community = calloc(n, sizeof(int));
+		r->count = n;
+		r->modularity = 0.0;
+		return r;
+	}
+
+	// each node starts in its own community
+	int *community = malloc(n * sizeof(int));
+	for (int i = 0; i < n; i++)
+		community[i] = i;
+
+	printf("[louvain] m = %.0f, n = %d\n", m, n);
+
+	int moves = phase1(graph, community, m);
+	printf("[louvain] phase 1 done — %d moves\n", moves);
+
+	double Q = compute_modularity(graph, community, m);
+	printf("[louvain] modularity Q = %.4f\n", Q);
+
+	int count = compact(community, n);
+	printf("[louvain] %d communities detected\n", count);
+
+	louvain_result_t *result = malloc(sizeof(louvain_result_t));
+	result->node_community = community;
+	result->count = count;
+	result->modularity = Q;
+	return result;
+}
+
+void free_louvain_result(louvain_result_t *result)
+{
+	if (!result)
+		return;
+	free(result->node_community);
+	free(result);
+}

main.c

@@ -1,17 +1,14 @@
 #include "structs.h"
 #include "render.h"
-#include <stdlib.h>
-#include <time.h>
 #include <SDL2/SDL.h>
 
 #define WINDOW_WIDTH 800
 #define WINDOW_HEIGHT 600
 
-int main(void)
+int main(int argc, char *argv[])
 {
-	srand(time(0));
-
-	graph_t *g = generate_graph(20, 1, 0.04);
+	// Figure 1
+	graph_t *g = generate_graph(20, 1, 0.04, 122);
 
 	SDL_Init(SDL_INIT_VIDEO);
 
@@ -21,7 +18,8 @@ int main(void)
 	SDL_Renderer *renderer =
 		SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
 
-	render_graph(renderer, g);
+	// Figure 2
+	render_graph(renderer, g, LOUVAIN);
 
 	SDL_Event e;
 	int running = 1;

render.c

@@ -1,3 +1,5 @@
+#include "render.h"
+#include "algorithms.h"
 #include "structs.h"
 #include <SDL2/SDL.h>
 #include <math.h>
@@ -19,7 +21,7 @@ typedef struct layout_node_t layout_node_t;
 // display a simple node of radius r
 static void draw_node(SDL_Renderer *renderer, int cx, int cy, int r)
 {
-	SDL_SetRenderDrawColor(renderer, 215, 153, 33, 255);
+	//SDL_SetRenderDrawColor(renderer, 215, 153, 33, 255);
 	for (int dy = -r; dy <= r; dy++) {
 		int dx = (int)sqrt((double)(r * r - dy * dy));
 		SDL_RenderDrawLine(renderer, cx - dx, cy + dy, cx + dx,
@@ -118,7 +120,19 @@ static layout_node_t *compute_layout(const graph_t *graph)
 	return nodes;
 }
 
-void render_graph(SDL_Renderer *renderer, const graph_t *graph)
+static SDL_Color community_colors[] = {
+	{ 251, 73, 52, 255 }, // gruvbox red
+	{ 250, 189, 47, 255 }, // gruvbox yellow
+	{ 142, 192, 124, 255 }, // gruvbox green
+	{ 131, 165, 152, 255 }, // gruvbox aqua
+	{ 69, 133, 136, 255 }, // gruvbox blue
+	{ 211, 134, 155, 255 }, // gruvbox pink
+	{ 254, 128, 25, 255 }, // gruvbox orange
+};
+#define N_COLORS (sizeof(community_colors) / sizeof(community_colors[0]))
+
+void render_graph(SDL_Renderer *renderer, const graph_t *graph,
+		  VISUALIZATION_TYPE type)
 {
 	if (!renderer || !graph || !graph->adj_lists)
 		return;
@@ -129,11 +143,21 @@ void render_graph(SDL_Renderer *renderer, const graph_t *graph)
 	if (!layout)
 		return;
 
-	// Clear background
+	community_result_t *communities = NULL;
+	louvain_result_t *louvain = NULL;
+
+	switch (type) {
+	case CLIQUE:
+		communities = find_k_clique_communities(graph, 3);
+		break;
+	case LOUVAIN:
+		louvain = compute_louvain(graph);
+		break;
+	}
+
 	SDL_SetRenderDrawColor(renderer, 48, 48, 48, 255);
 	SDL_RenderClear(renderer);
 
-	// Draw edges
 	SDL_SetRenderDrawColor(renderer, 189, 189, 189, 255);
 	for (int i = 0; i < n; i++) {
 		node_t *neighbor = graph->adj_lists[i];
@@ -155,10 +179,34 @@ void render_graph(SDL_Renderer *renderer, const graph_t *graph)
 		int x = (int)layout[i].x;
 		int y = (int)layout[i].y;
 
+		int c;
+		SDL_Color col;
+
+		switch (type) {
+		case CLIQUE:
+			c = communities->node_community[i];
+			col = (c == -1) ? (SDL_Color){ 150, 150, 150, 255 } :
+					  community_colors[c % N_COLORS];
+			break;
+		case LOUVAIN:
+			c = louvain->node_community[i];
+			col = (c == -1) ? (SDL_Color){ 168, 153, 132, 255 } :
+					  community_colors[c % N_COLORS];
+			break;
+		}
+		SDL_SetRenderDrawColor(renderer, col.r, col.g, col.b, col.a);
+
 		// Node fill
 		draw_node(renderer, x, y, NODE_RADIUS);
 	}
 
+	if (communities != NULL) {
+		free_community_result(communities);
+	}
+	if (louvain != NULL) {
+		free_louvain_result(louvain);
+	}
+
 	free(layout);
 	SDL_RenderPresent(renderer);
 }

render.h

@@ -1,4 +1,17 @@
+//
+// Created by Tiago Batista Cardoso on 2/23/2026.
+//
+
+#ifndef GRAPHE_RENDER_H
+#define GRAPHE_RENDER_H
+
 #include "structs.h"
 #include <SDL2/SDL_render.h>
 
-void render_graph(SDL_Renderer *renderer, const graph_t *graph);
+enum VISUALIZATION_TYPE { CLIQUE, LOUVAIN };
+typedef enum VISUALIZATION_TYPE VISUALIZATION_TYPE;
+
+void render_graph(SDL_Renderer *renderer, const graph_t *graph,
+		  VISUALIZATION_TYPE);
+
+#endif

structs.c

@@ -28,19 +28,6 @@ graph_t *create_graph(int n, double p, double q)
 	return new_graph;
 }
 
-//void add_edge(graph_t *graph, int src, int dest)
-//{
-//	// src -> dest
-//	node_t *new_node = create_node(dest);
-//	new_node->next = graph->adj_lists[src];
-//	graph->adj_lists[src] = new_node;
-//
-//	// dest -> src
-//	new_node = create_node(src);
-//	new_node->next = graph->adj_lists[dest];
-//	graph->adj_lists[dest] = new_node;
-//}
-
 void add_edge(graph_t *graph, int src, int dest)
 {
 	// Guard against self-loops and out-of-bounds
@@ -89,7 +76,7 @@ graph_t *basic_graph()
 	return basic;
 }
 
-graph_t *generate_graph(int n, double p, double q)
+graph_t *generate_graph(int n, double p, double q, int seed)
 {
 	clock_t start, end;
 	double cpu_time_used;
@@ -100,6 +87,8 @@ graph_t *generate_graph(int n, double p, double q)
 	graph_t *result = create_graph(n, p, q);
 	int remaining = n;
 
+	srand(seed);
+
 	// Calcul des repartitions aleatoires
 	int n1 = rand() % (remaining + 1);
 	remaining -= n1;

structs.h

@@ -24,7 +24,7 @@ node_t *create_node(int id);
 graph_t *create_graph(int n, double p, double q);
 void add_edge(graph_t *graph, int src, int dest);
 graph_t *basic_graph();
-graph_t *generate_graph(int n, double p, double q);
+graph_t *generate_graph(int n, double p, double q, int seed);
 void displayGraph(graph_t *graph);
 void free_graph(graph_t *graph);