42 lines
1.7 KiB
C
42 lines
1.7 KiB
C
#include "cs.h"
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/* find the strongly connected components of a square matrix */
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csd *cs_scc (cs *A) /* matrix A temporarily modified, then restored */
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{
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int n, i, k, b, nb = 0, top, *xi, *pstack, *p, *r, *Ap, *ATp, *rcopy, *Blk ;
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cs *AT ;
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csd *D ;
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if (!CS_CSC (A)) return (NULL) ; /* check inputs */
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n = A->n ; Ap = A->p ;
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D = cs_dalloc (n, 0) ; /* allocate result */
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AT = cs_transpose (A, 0) ; /* AT = A' */
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xi = cs_malloc (2*n+1, sizeof (int)) ; /* get workspace */
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if (!D || !AT || !xi) return (cs_ddone (D, AT, xi, 0)) ;
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Blk = xi ; rcopy = pstack = xi + n ;
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p = D->p ; r = D->r ; ATp = AT->p ;
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top = n ;
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for (i = 0 ; i < n ; i++) /* first dfs(A) to find finish times (xi) */
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{
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if (!CS_MARKED (Ap, i)) top = cs_dfs (i, A, top, xi, pstack, NULL) ;
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}
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for (i = 0 ; i < n ; i++) CS_MARK (Ap, i) ; /* restore A; unmark all nodes*/
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top = n ;
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nb = n ;
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for (k = 0 ; k < n ; k++) /* dfs(A') to find strongly connnected comp */
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{
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i = xi [k] ; /* get i in reverse order of finish times */
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if (CS_MARKED (ATp, i)) continue ; /* skip node i if already ordered */
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r [nb--] = top ; /* node i is the start of a component in p */
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top = cs_dfs (i, AT, top, p, pstack, NULL) ;
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}
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r [nb] = 0 ; /* first block starts at zero; shift r up */
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for (k = nb ; k <= n ; k++) r [k-nb] = r [k] ;
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D->nb = nb = n-nb ; /* nb = # of strongly connected components */
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for (b = 0 ; b < nb ; b++) /* sort each block in natural order */
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{
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for (k = r [b] ; k < r [b+1] ; k++) Blk [p [k]] = b ;
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}
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for (b = 0 ; b <= nb ; b++) rcopy [b] = r [b] ;
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for (i = 0 ; i < n ; i++) p [rcopy [Blk [i]]++] = i ;
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return (cs_ddone (D, AT, xi, 1)) ;
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}
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