From 090a9393e4b3076391bd73d183021d5bde3209e4 Mon Sep 17 00:00:00 2001
From: Kohei Morita <yosupo06@gmail.com>
Date: Tue, 22 Sep 2020 14:22:55 +0900
Subject: [PATCH] fix #51: add assert for mcf_graph.add_edge

---
 atcoder/mincostflow.hpp            | 2 ++
 test/unittest/mincostflow_test.cpp | 9 ++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/atcoder/mincostflow.hpp b/atcoder/mincostflow.hpp
index 1db2f9e..f7bfc9f 100644
--- a/atcoder/mincostflow.hpp
+++ b/atcoder/mincostflow.hpp
@@ -17,6 +17,8 @@ template <class Cap, class Cost> struct mcf_graph {
     int add_edge(int from, int to, Cap cap, Cost cost) {
         assert(0 <= from && from < _n);
         assert(0 <= to && to < _n);
+        assert(0 <= cap);
+        assert(0 <= cost);
         int m = int(pos.size());
         pos.push_back({from, int(g[from].size())});
         int from_id = int(g[from].size());
diff --git a/test/unittest/mincostflow_test.cpp b/test/unittest/mincostflow_test.cpp
index fdf027d..ea31e7c 100644
--- a/test/unittest/mincostflow_test.cpp
+++ b/test/unittest/mincostflow_test.cpp
@@ -87,4 +87,11 @@ TEST(MincostflowTest, SameCostPaths) {
     ASSERT_EQ(2, g.add_edge(0, 2, 2, 1));
     auto expected = std::vector<std::pair<int, int>>{{0, 0}, {3, 3}};
     ASSERT_EQ(expected, g.slope(0, 2));
-}
\ No newline at end of file
+}
+
+TEST(MincostflowTest, Invalid) {
+    mcf_graph<int, int> g(2);
+    // https://github.com/atcoder/ac-library/issues/51
+    EXPECT_DEATH(g.add_edge(0, 0, -1, 0), ".*");
+    EXPECT_DEATH(g.add_edge(0, 0, 0, -1), ".*");
+}