public static void main ( String [ ] args ) {
  Scanner in = new Scanner ( System . in ) ;
  N = Integer . parseInt ( in . next ( ) ) ;
  a = Integer . parseInt ( in . next ( ) ) - 1 ;
  b = Integer . parseInt ( in . next ( ) ) - 1 ;
  M = Integer . parseInt ( in . next ( ) ) ;
  E = new ArrayList [ N ] ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    E [ i ] = new ArrayList < > ( ) ;
  }
  for ( int i = 0 ;
  i < M ;
  i ++ ) {
    int x = Integer . parseInt ( in . next ( ) ) - 1 ;
    int y = Integer . parseInt ( in . next ( ) ) - 1 ;
    E [ x ] . add ( y ) ;
    E [ y ] . add ( x ) ;
  }
  long [ ] cost = new long [ N ] ;
  long [ ] count = new long [ N ] ;
  boolean [ ] visited = new boolean [ N ] ;
  Arrays . fill ( cost , INF ) ;
  Queue < Integer > q = new ArrayDeque < > ( ) ;
  q . add ( a ) ;
  cost [ a ] = 0 ;
  count [ a ] = 1 ;
  visited [ a ] = true ;
  while ( ! q . isEmpty ( ) ) {
    int st = q . remove ( ) ;
    for ( int adj : E [ st ] ) {
      if ( cost [ st ] + 1 <= cost [ adj ] ) {
        cost [ adj ] = cost [ st ] + 1 ;
        count [ adj ] += count [ st ] ;
        if ( ! visited [ adj ] ) {
          q . add ( adj ) ;
        }
        visited [ adj ] = true ;
      }
    }
  }
  System . out . println ( count [ b ] % MODP ) ;
}

public static void main ( String [ ] args ) { Scanner in = new Scanner ( System . in ) ; N = Integer . parseInt ( in . next ( ) ) ; a = Integer . parseInt ( in . next ( ) ) - 1 ; b = Integer . parseInt ( in . next ( ) ) - 1 ; M = Integer . parseInt ( in . next ( ) ) ; E = new ArrayList [ N ] ; for ( int i = 0 ; i < N ; i ++ ) { E [ i ] = new ArrayList < > ( ) ; } for ( int i = 0 ; i < M ; i ++ ) { int x = Integer . parseInt ( in . next ( ) ) - 1 ; int y = Integer . parseInt ( in . next ( ) ) - 1 ; E [ x ] . add ( y ) ; E [ y ] . add ( x ) ; } long [ ] cost = new long [ N ] ; long [ ] count = new long [ N ] ; boolean [ ] visited = new boolean [ N ] ; Arrays . fill ( cost , INF ) ; Queue < Integer > q = new ArrayDeque < > ( ) ; q . add ( a ) ; cost [ a ] = 0 ; count [ a ] = 1 ; visited [ a ] = true ; while ( ! q . isEmpty ( ) ) { int st = q . remove ( ) ; for ( int adj : E [ st ] ) { if ( cost [ st ] + 1 <= cost [ adj ] ) { cost [ adj ] = cost [ st ] + 1 ; count [ adj ] += count [ st ] ; if ( ! visited [ adj ] ) { q . add ( adj ) ; } visited [ adj ] = true ; } } } System . out . println ( count [ b ] % MODP ) ; }
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