From 8f8426b4f887b046990cde095969235d735d38cb Mon Sep 17 00:00:00 2001
From: Jens Gerlach <jens.gerlach@fokus.fraunhofer.de>
Date: Tue, 24 Nov 2015 15:13:46 +0100
Subject: [PATCH] compute permutations by std::next_permutation

---
 src/util.cpp | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/src/util.cpp b/src/util.cpp
index de8f73571..6e4d89d48 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -36,6 +36,7 @@
 #include <sstream>
 #include <cassert>
 #include <vector>
+#include <algorithm>
 #include "OutputMgr.h"
 #include "AbsProgramGenerator.h"
 #include "CGOptions.h"
@@ -81,28 +82,22 @@ gensym(const string& basename)
  */
 vector<intvec> permute(intvec in)
 {
-	vector<intvec> out;
 	/* basic cases */
-	if (in.size()==0) return out;
+	std::vector<intvec> out;
+	if (in.size() == 0) {
+		return out;
+        }
+
+	out.push_back(in);
 	if (in.size() == 1) {
-		out.push_back(in);
 		return out;
 	}
-	/* extended cases: divide the array into head and tail, permute
-	   tail, then insert head into all possible positions in tail */
-	int head = in[0];
-	intvec tail = in;
-	tail.erase(tail.begin());
-	vector<intvec> tails = permute(tail);
-	size_t i, j;
-	for (i=0; i<tails.size(); i++) {
-		intvec one_tail = tails[i];
-		for (j=0; j<=one_tail.size(); j++) {
-			intvec tmp = one_tail;
-			tmp.insert(tmp.begin()+j, head);
-			out.push_back(tmp);
-		}
-	}
+
+        // generate all permutations from 'in'
+        while(std::next_permutation(in.begin(), in.end())) {
+		out.push_back(in);
+        }
+
 	return out;
 }