cKit/Graph/c_GabowSCC.c

#include <c_GabowSCC.h>


static void c_GabowSCC_DFS(c_GabowSCC_t* self, c_Digraph_t* graph, c_size_t v) {
    self->marked[v] = C_TRUE;
    self->pre[v] = self->pre_counter++;

    /* Push onto both structural tracking stacks */
    self->scc_stack[self->scc_stack_sz++] = v;
    self->path_stack[self->path_stack_sz++] = v;

    c_AdjList_t* adj = &graph->adj_list[v];
    c_size_t size = (c_size_t)c_UIntArray_GetSize(adj);

    for (c_size_t i = 0; i < size; ++i) {
        c_uint_t target_value = 0;
        c_err_t err = c_UIntArray_Get(adj, i, &target_value);

        if (err == C_SUCCESS) {
            c_size_t w = (c_size_t)target_value;

            if (!self->marked[w]) {
                c_GabowSCC_DFS(self, graph, w);
            }
            /* If already visited but not yet assigned to an SCC component */
            else if (self->id[w] == C_SIZE_MAX) {
                /* Pop vertices from path_stack whose pre-order numbers are greater than pre[w] */
                while (self->path_stack_sz > 0 && self->pre[self->path_stack[self->path_stack_sz - 1]] > self->pre[w]) {
                    self->path_stack_sz--;
                }
            }
        }
    }

    /* If v is the root of an SCC component block, pop the complete component cluster */
    if (self->path_stack_sz > 0 && self->path_stack[self->path_stack_sz - 1] == v) {
        self->path_stack_sz--; /* Remove v from the root boundary stack */

        c_size_t w = 0;
        do {
            w = self->scc_stack[--self->scc_stack_sz];
            self->id[w] = self->count;
        } while (w != v);

        self->count++; /* Increment structural component counter group */
    }
}

c_err_t c_GabowSCC_Init(c_GabowSCC_t* self, c_Digraph_t* graph, c_Allocator_t* allocator) {
    if (!self || !graph) return C_ERR_PARAM;

    self->allocator = allocator ? *allocator : c_DefaultAllocator;
    self->count = 0;
    self->pre_counter = 0;
    self->scc_stack_sz = 0;
    self->path_stack_sz = 0;
    self->V = graph->V;

    if (self->V == 0) return C_SUCCESS;

    /* 1. Allocate tracked execution matrices arrays */
    self->marked     = (c_bool_t*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(c_bool_t));
    self->id         = (c_size_t*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(c_size_t));
    self->pre        = (c_size_t*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(c_size_t));
    self->scc_stack  = (c_size_t*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(c_size_t));
    self->path_stack = (c_size_t*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(c_size_t));

    if (!self->marked || !self->id || !self->pre || !self->scc_stack || !self->path_stack) {
        c_GabowSCC_Destroy(self);
        return C_ERR_NOMEM;
    }

    /* Initialize all ID components to unassigned boundary sentinel state */
    for (c_size_t i = 0; i < self->V; ++i) {
        self->id[i] = C_SIZE_MAX;
    }

    /* 2. Process all components loops securely */
    for (c_size_t v = 0; v < self->V; ++v) {
        if (!self->marked[v]) {
            c_GabowSCC_DFS(self, graph, v);
        }
    }

    return C_SUCCESS;
}

void c_GabowSCC_Destroy(c_GabowSCC_t* self) {
    if (!self) return;
    if (self->marked)     c_Allocator_Free(&self->allocator, self->marked);
    if (self->id)         c_Allocator_Free(&self->allocator, self->id);
    if (self->pre)        c_Allocator_Free(&self->allocator, self->pre);
    if (self->scc_stack)  c_Allocator_Free(&self->allocator, self->scc_stack);
    if (self->path_stack) c_Allocator_Free(&self->allocator, self->path_stack);

    self->marked = NULL;
    self->id = NULL;
    self->pre = NULL;
    self->scc_stack = NULL;
    self->path_stack = NULL;
    self->count = 0;
    self->scc_stack_sz = 0;
    self->path_stack_sz = 0;
    self->V = 0;
}