/* File MinPriorityQueue.c. */

#include "mcs360.h"
#include "MinPriorityQueue.h"

struct MinPriorityQueue {
    int size;                 /* Current size of MinPriorityQueue. */
    int capacity;             /* Allocated size of dynamic array. */
    PQEntry *entry;           /* Dynamic array for MinPriorityQueue entries. */
    Boolean (*less)(PQEntry a,  /* Pointer to function returning true if first */
                    PQEntry b); /*   argument is treated as less than the second. */
};

#define INITIAL_CAPACITY 16


MinPriorityQueue *CreateMinPriorityQueue( Boolean (*less)(PQEntry,PQEntry))
{
    MinPriorityQueue *newPQ = (MinPriorityQueue *)checked_malloc(sizeof(MinPriorityQueue));
    newPQ->size = 0;
    newPQ->capacity = INITIAL_CAPACITY;
    newPQ->entry = (PQEntry *)checked_malloc( newPQ->capacity * sizeof(PQEntry));
    newPQ->less = less;
    return newPQ;
}

void DestroyMinPriorityQueue( MinPriorityQueue *pq)
{
    free( pq->entry);
    free(pq);
}

void add( PQEntry item, MinPriorityQueue *pq)
{
    int n;
    if (pq->size == pq->capacity ) {
        pq->entry = (PQEntry *)checked_realloc( pq->entry, 2*pq->capacity);
        pq->capacity *= 2;
    }
    ++pq->size;
    n = pq->size - 1;
    pq->entry[n] = item;
    while ( n > 0 && pq->less( pq->entry[n], pq->entry[(n-1)/2]) ) {
        PQEntry temp = pq->entry[n];
        pq->entry[n] = pq->entry[(n-1)/2];
        pq->entry[(n-1)/2] = temp;
        n = (n-1) / 2;
    }
}

PQEntry removeMin( MinPriorityQueue *pq)
{
    int i, smallest;
    PQEntry minEntry = pq->entry[0];
    pq->entry[0] = pq->entry[--pq->size];
    i = 0;
    while ( 2*i+1 <= pq->size - 1 ) {
        smallest = i;
        if ( pq->less( pq->entry[2*i+1], pq->entry[i]) )
            smallest = 2*i+1;
        if ( 2*i+2 <= pq->size-1 && less( pq->entry[2*i+2], pq->entry[smallest]) )
            smallest = 2*i+2;
        if ( smallest != i ) {
            PQEntry temp = pq->entry[i];
            pq->entry[i] = pq->entry[smallest];
            pq->entry[smallest] = temp;
            i = smallest;
        }
        else
            i = pq->size;
    }
    return minEntry;
}

PQEntry min( const MinPriorityQueue *pq)
{
    return pq->entry[0];
}

Boolean empty( const MinPriorityQueue *pq)
{
    return pq->size == 0;
}

int size( const MinPriorityQueue *pq)
{
    return pq->size;
}