tasks a-s

Task/Permutations/R/permutations.r

@@ -0,0 +1,48 @@
+next.perm <- function(p) {
+	n <- length(p)
+	i <- n - 1
+	r = TRUE
+	for(i in (n-1):1) {
+		if(p[i] < p[i+1]) {
+			r = FALSE
+			break
+		}
+	}
+	
+	j <- i + 1
+	k <- n
+	while(j < k) {
+		x <- p[j]
+		p[j] <- p[k]
+		p[k] <- x
+		j <- j + 1
+		k <- k - 1
+	}
+	
+	if(r) return(NULL)
+	
+	j <- n
+	while(p[j] > p[i]) j <- j - 1
+	j <- j + 1
+	
+	x <- p[i]
+	p[i] <- p[j]
+	p[j] <- x
+	return(p)
+}
+
+print.perms <- function(n) {
+	p <- 1:n
+	while(!is.null(p)) {
+		cat(p,"\n")
+		p <- next.perm(p)
+	}
+}
+
+print.perms(3)
+# 1 2 3
+# 1 3 2
+# 2 1 3
+# 2 3 1
+# 3 1 2
+# 3 2 1