From 1ca9100261b8c27cf62acccc3618c5e8375bf57b Mon Sep 17 00:00:00 2001
From: Kohei Morita <yosupo06@gmail.com>
Date: Fri, 11 Sep 2020 03:14:03 +0900
Subject: [PATCH] fix issue #1

---
 atcoder/maxflow.hpp                | 7 +++++--
 atcoder/mincostflow.hpp            | 7 +++++--
 test/unittest/maxflow_test.cpp     | 9 +++++++++
 test/unittest/mincostflow_test.cpp | 9 +++++++++
 4 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/atcoder/maxflow.hpp b/atcoder/maxflow.hpp
index 02f2354..2b69899 100644
--- a/atcoder/maxflow.hpp
+++ b/atcoder/maxflow.hpp
@@ -21,8 +21,11 @@ template <class Cap> struct mf_graph {
         assert(0 <= cap);
         int m = int(pos.size());
         pos.push_back({from, int(g[from].size())});
-        g[from].push_back(_edge{to, int(g[to].size()), cap});
-        g[to].push_back(_edge{from, int(g[from].size()) - 1, 0});
+        int from_id = int(g[from].size());
+        int to_id = int(g[to].size());
+        if (from == to) to_id++;
+        g[from].push_back(_edge{to, to_id, cap});
+        g[to].push_back(_edge{from, from_id, 0});
         return m;
     }
 
diff --git a/atcoder/mincostflow.hpp b/atcoder/mincostflow.hpp
index da0eefb..321f3e1 100644
--- a/atcoder/mincostflow.hpp
+++ b/atcoder/mincostflow.hpp
@@ -19,8 +19,11 @@ template <class Cap, class Cost> struct mcf_graph {
         assert(0 <= to && to < _n);
         int m = int(pos.size());
         pos.push_back({from, int(g[from].size())});
-        g[from].push_back(_edge{to, int(g[to].size()), cap, cost});
-        g[to].push_back(_edge{from, int(g[from].size()) - 1, 0, -cost});
+        int from_id = int(g[from].size());
+        int to_id = int(g[to].size());
+        if (from == to) to_id++;
+        g[from].push_back(_edge{to, to_id, cap, cost});
+        g[to].push_back(_edge{from, from_id, 0, -cost});
         return m;
     }
 
diff --git a/test/unittest/maxflow_test.cpp b/test/unittest/maxflow_test.cpp
index 250d860..4318dd8 100644
--- a/test/unittest/maxflow_test.cpp
+++ b/test/unittest/maxflow_test.cpp
@@ -169,3 +169,12 @@ TEST(MaxflowTest, BoundUint) {
     e = {0, 2, INF, INF};
     edge_eq(e, g.get_edge(2));
 }
+
+// https://github.com/atcoder/ac-library/issues/1
+TEST(MaxflowTest, SelfLoop) {
+    mf_graph<int> g(3);
+    ASSERT_EQ(0, g.add_edge(0, 0, 100));
+
+    mf_graph<int>::edge e = {0, 0, 100, 0};
+    edge_eq(e, g.get_edge(0));
+}
diff --git a/test/unittest/mincostflow_test.cpp b/test/unittest/mincostflow_test.cpp
index c8c2688..baec43f 100644
--- a/test/unittest/mincostflow_test.cpp
+++ b/test/unittest/mincostflow_test.cpp
@@ -70,3 +70,12 @@ TEST(MincostflowTest, OutOfRange) {
     EXPECT_DEATH(g.slope(-1, 3), ".*");
     EXPECT_DEATH(g.slope(3, 3), ".*");
 }
+
+// https://github.com/atcoder/ac-library/issues/1
+TEST(MaxflowTest, SelfLoop) {
+    mcf_graph<int, int> g(3);
+    ASSERT_EQ(0, g.add_edge(0, 0, 100, 123));
+
+    mcf_graph<int, int>::edge e = {0, 0, 100, 0, 123};
+    edge_eq(e, g.get_edge(0));
+}