formulaIsRight <- function( x ){
	left <- x[1]*(10*x[2]+x[3])+100*x[4]+10*x[5]+x[6]
	right <- 1000*x[7]+100*x[8]+10*x[9]+x[10]
	return( left == right )
}
 
# count <<- 0, permutation( 0:9, NULL ) で呼び出す
permutation <- function( s, a ){
	if( length( s ) <= 0 ){
		if( formulaIsRight( a ) ){
			count <<- count + 1
		}
	}else{
		for( i in s ){
			Recall( s[ s != i ], c( a, i ) )
		}
	}
}
 
count <<- 0
permutation( 0:9, NULL )
print( count ) # 350

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