tasks a-s

Task/N-queens-problem/R/n-queens-problem.r

@@ -0,0 +1,28 @@
+# Brute force, see the "Permutations" page for the next.perm function
+safe <- function(p) {
+	n <- length(p)
+	for(i in 1:(n-1)) {
+		for(j in (i+1):n) {
+			if(abs(p[j] - p[i]) == abs(j - i)) return(FALSE)
+		}
+	}
+	return(TRUE)
+}
+
+queens <- function(n) {
+	p <- 1:n
+	k <- 0
+	while(!is.null(p)) {
+		if(safe(p)) {
+			cat(p,"\n")
+			k <- k + 1
+		}
+		p <- next.perm(p)
+	}
+	return(k)
+}
+
+queens(8)
+# 1 5 8 6 3 7 2 4
+# ...
+# 92