Graph

Graph/c_NonrecursiveDirectedDFS.c

@@ -0,0 +1,88 @@
+#include <c_NonrecursiveDirectedDFS.h>
+#include <c_ArrayStack.h>
+
+typedef struct {
+    c_size_t v;           /* Current vertex */
+    c_size_t edge_idx;    /* Next neighbor index to examine in the adjacency list */
+} c_DFSFrame_t;
+
+c_err_t c_NonrecursiveDirectedDFS_Init(c_NonrecursiveDirectedDFS_t* self, c_Digraph_t* graph, c_size_t s, c_Allocator_t* allocator) {
+    if (!self || !graph || s >= graph->V) return C_ERR_PARAM;
+
+    self->allocator = allocator?*allocator:c_DefaultAllocator;
+    self->count = 0;
+
+    /* 1. Allocate the visited tracking array */
+    self->marked = (c_bool_t*)c_Allocator_Calloc(&self->allocator, graph->V, sizeof(c_bool_t));
+    if (!self->marked) return C_ERR_NOMEM;
+
+    /* 2. Allocate an explicit execution stack bounded exactly by the number of vertices O(V) */
+    c_DFSFrame_t frame={0};
+
+    c_ArrayStack_t stack;
+    c_err_t err = c_ArrayStack_Init(&stack, sizeof(c_DFSFrame_t), 0, allocator);
+    if (err!=C_ERR_OK) {
+        c_Allocator_Free(&self->allocator, self->marked);
+        self->marked = NULL;
+        return err;
+    }
+
+    /* Push the initial source vertex frame onto our stack */
+    self->marked[s] = C_TRUE;
+    self->count++;
+
+    frame.v = s;
+    frame.edge_idx = 0;
+    c_ArrayStack_Push(&stack, &frame);
+
+    /* 3. Non-recursive processing loop */
+    while (!c_ArrayStack_IsEmpty(&stack)) {
+        /* Peek the top frame */
+        c_DFSFrame_t* current_frame = c_ArrayStack_Peek(&stack);
+
+        c_size_t u = current_frame->v;
+
+        c_AdjList_t* adj = &graph->adj_list[u];
+        c_size_t neighbor_count = (c_size_t)c_AdjList_GetSize(adj);
+
+        /* Advance down the adjacency list until we find an unvisited neighbor or finish the list */
+        c_bool_t advanced = C_FALSE;
+        while (current_frame->edge_idx < neighbor_count) {
+            c_size_t w;
+            c_AdjList_Get(adj, current_frame->edge_idx, &w);
+            current_frame->edge_idx++; /* Increment pointer for next pass */
+
+            if (!self->marked[w]) {
+                self->marked[w] = C_TRUE;
+                self->count++;
+
+                /* Push new frame onto the stack (equivalent to recursive call invocation) */
+                frame.v = w;
+                frame.edge_idx = 0;
+                c_ArrayStack_Push(&stack, &frame);
+
+                advanced = C_TRUE;
+                break;
+            }
+        }
+
+        /* If we explored all neighbors of vertex u, pop it from the stack */
+        if (!advanced) {
+            c_ArrayStack_Pop(&stack, 0);
+        }
+    }
+
+    /* Clean up the runtime frame stack buffer */
+    c_ArrayStack_Destroy(&stack);
+    return C_SUCCESS;
+}
+
+void c_NonrecursiveDirectedDFS_Destroy(c_NonrecursiveDirectedDFS_t* self) {
+    if (!self) return;
+    if (self->marked) {
+        c_Allocator_Free(&self->allocator, self->marked);
+        self->marked = NULL;
+    }
+    self->count = 0;
+}
+