cKit/Graph/c_PrimMST.c

#include <c_PrimMST.h>
#include "c_IndexMinPQ.h"

#define PQ_SENTINEL ((c_size_t)-1)

/* ================================================================================================================== */
/* Private Comparison Callback for c_IndexMinPQ_t */

static int c_Prim_WeightCompare(const void* a, const void* b, void* args) {
    double w_a = *(const double*)a;
    double w_b = *(const double*)b;
    (void)args;

    return (w_a > w_b) - (w_a < w_b);
}

/* ================================================================================================================== */
/* Eager Prim Scanning Subroutine Processing Functions */

static void c_Prim_Scan(c_PrimMST_t* self, const c_EdgeWeightedGraph_t* graph, c_size_t v, c_IndexMinPQ_t* pq) {
    self->marked[v] = C_TRUE;

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

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

        if (err == C_SUCCESS) {
            c_size_t edge_id = (c_size_t)generic_edge_id;
            c_Edge_t* edge = &graph->edges_pool[edge_id];
            c_size_t w = (edge->v == v) ? edge->w : edge->v;

            if (self->marked[w]) continue;

            if (edge->weight < self->dist_to[w]) {
                self->dist_to[w] = edge->weight;
                self->edge_to[w] = edge_id;

                /* Leverage clean generic membership checking and modification mutations */
                if (c_IndexMinPQ_Contains(pq, w)) {
                    c_IndexMinPQ_Change(pq, w, &self->dist_to[w]);
                } else {
                    c_IndexMinPQ_Push(pq, w, &self->dist_to[w]);
                }
            }
        }
    }
}

c_err_t c_PrimMST_Init(c_PrimMST_t* self, c_EdgeWeightedGraph_t* graph, c_Allocator_t* allocator) {
    if (!self || !graph) return C_ERR_PARAM;

    self->allocator = allocator ? *allocator : c_DefaultAllocator;
    self->weight = 0.0;
    self->V = graph->V;
    c_VertexIdList_Init(&self->mst_edges, 0, allocator);

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

    /* 1. Allocate primary evaluation buffers */
    self->marked  = (c_bool_t*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(c_bool_t));
    self->edge_to = (c_size_t*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(c_size_t));
    self->dist_to = (double*)c_Allocator_Calloc(&self->allocator, self->V, sizeof(double));

    if (!self->marked || !self->edge_to || !self->dist_to) {
        c_PrimMST_Destroy(self);
        return C_ERR_NOMEM;
    }

    /* Initialize metrics tracking layouts to positive infinity benchmarks */
    for (c_size_t v = 0; v < self->V; ++v) {
        self->dist_to[v] = DBL_MAX;
        self->edge_to[v] = PQ_SENTINEL;
    }

    /* 2. Configure your formal generic Index Priority Queue sized exactly to V vertices */
    c_IndexMinPQ_t pq;
    c_err_t err = c_IndexMinPQ_Init(
        &pq,
        self->V,
        sizeof(double),
        c_Prim_WeightCompare,
        NULL,
        allocator
    );

    if (err != C_SUCCESS) {
        c_PrimMST_Destroy(self);
        return err;
    }

    /* 3. Run search loops across vertices to handle potential spanning forests */
    for (c_size_t v = 0; v < self->V; ++v) {
        if (!self->marked[v]) {
            self->dist_to[v] = 0.0;
            c_IndexMinPQ_Push(&pq, v, &self->dist_to[v]);

            while (pq.size > 0) {
                c_size_t curr_v = 0;
                c_IndexMinPQ_Pop(&pq, &curr_v);

                /* Accumulate tree weights if it is not a structural forest root node */
                if (self->edge_to[curr_v] != PQ_SENTINEL) {
                    c_VertexIdList_Append(&self->mst_edges, (c_uint_t)self->edge_to[curr_v]);
                    self->weight += self->dist_to[curr_v];
                }

                c_Prim_Scan(self, graph, curr_v, &pq);
            }
        }
    }

    /* Clean up index priority queue allocations */
    c_IndexMinPQ_Destroy(&pq);
    return C_SUCCESS;
}

void c_PrimMST_Destroy(c_PrimMST_t* self) {
    if (!self) return;
    if (self->marked)  c_Allocator_Free(&self->allocator, self->marked);
    if (self->edge_to) c_Allocator_Free(&self->allocator, self->edge_to);
    if (self->dist_to) c_Allocator_Free(&self->allocator, self->dist_to);

    c_VertexIdList_Destroy(&self->mst_edges);

    self->marked = NULL;
    self->edge_to = NULL;
    self->dist_to = NULL;
    self->weight = 0.0;
    self->V = 0;
}

c_err_t c_PrimMST_GetEdges(c_PrimMST_t* self, c_VertexIdList_t* out_edges) {
    if (!self || !out_edges) return C_ERR_PARAM;
    return c_VertexIdList_Copy(out_edges, &self->mst_edges);
}