cs_dfs.c

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#include "cs.h"
/* depth-first-search of the graph of a matrix, starting at node j */
int cs_dfs (int j, cs *G, int top, int *xi, int *pstack, const int *pinv)
{
    int i, p, p2, done, jnew, head = 0, *Gp, *Gi ;
    if (!CS_CSC (G) || !xi || !pstack) return (-1) ;    /* check inputs */
    Gp = G->p ; Gi = G->i ;
    xi [0] = j ;                /* initialize the recursion stack */
    while (head >= 0)
    {
        j = xi [head] ;         /* get j from the top of the recursion stack */
        jnew = pinv ? (pinv [j]) : j ;
        if (!CS_MARKED (Gp, j))
        {
            CS_MARK (Gp, j) ;       /* mark node j as visited */
            pstack [head] = (jnew < 0) ? 0 : CS_UNFLIP (Gp [jnew]) ;
        }
        done = 1 ;                  /* node j done if no unvisited neighbors */
        p2 = (jnew < 0) ? 0 : CS_UNFLIP (Gp [jnew+1]) ;
        for (p = pstack [head] ; p < p2 ; p++)  /* examine all neighbors of j */
        {
            i = Gi [p] ;            /* consider neighbor node i */
            if (CS_MARKED (Gp, i)) continue ;   /* skip visited node i */
            pstack [head] = p ;     /* pause depth-first search of node j */
            xi [++head] = i ;       /* start dfs at node i */
            done = 0 ;              /* node j is not done */
            break ;                 /* break, to start dfs (i) */
        }
        if (done)               /* depth-first search at node j is done */
        {
            head-- ;            /* remove j from the recursion stack */
            xi [--top] = j ;    /* and place in the output stack */
        }
    }
    return (top) ;
}