From 4c4de31c2da02743084d6de996dc6a91877ad060 Mon Sep 17 00:00:00 2001
From: hitonanode <32937551+hitonanode@users.noreply.github.com>
Date: Sun, 6 Sep 2026 19:06:17 +0900
Subject: [PATCH] fix simplex

---
 combinatorial_opt/simplex.hpp                 |  6 +--
 .../test/simplex.yuki3674.test.cpp            | 51 +++++++++++++++++++
 2 files changed, 54 insertions(+), 3 deletions(-)
 create mode 100644 combinatorial_opt/test/simplex.yuki3674.test.cpp

diff --git a/combinatorial_opt/simplex.hpp b/combinatorial_opt/simplex.hpp
index fecf0c0c..c7ea5888 100644
--- a/combinatorial_opt/simplex.hpp
+++ b/combinatorial_opt/simplex.hpp
@@ -47,11 +47,11 @@ template <typename Float = double, int DEPS = 30, bool Randomize = true> struct
                 for (int j = 0; j < N + 2; j++) {
                     if (j != j_ch) {
                         mat[i_ch][j] *= -mat[i_ch][j_ch];
-                        if (abs_(mat[i_ch][j]) > EPS) jupd.push_back(j);
+                        if (mat[i_ch][j] != 0) jupd.push_back(j);
                     }
                 }
                 for (int i = 0; i < M + 2; i++) {
-                    if (abs_(mat[i][j_ch]) < EPS or i == i_ch) continue;
+                    if (mat[i][j_ch] == 0 or i == i_ch) continue;
                     for (auto j : jupd) mat[i][j] += mat[i][j_ch] * mat[i_ch][j];
                     mat[i][j_ch] *= mat[i_ch][j_ch];
                 }
@@ -76,7 +76,7 @@ template <typename Float = double, int DEPS = 30, bool Randomize = true> struct
                         i_ch = i;
                     } else if (mat[i_ch][N + 1] / mat[i_ch][j_ch] - mat[i][N + 1] / mat[i][j_ch] <
                                    EPS and
-                               idx[i_ch] > idx[i]) {
+                               idx[N + 1 + i_ch] > idx[N + 1 + i]) {
                         i_ch = i;
                     }
                 }
diff --git a/combinatorial_opt/test/simplex.yuki3674.test.cpp b/combinatorial_opt/test/simplex.yuki3674.test.cpp
new file mode 100644
index 00000000..e9b8198b
--- /dev/null
+++ b/combinatorial_opt/test/simplex.yuki3674.test.cpp
@@ -0,0 +1,51 @@
+#define PROBLEM "https://yukicoder.me/problems/no/3674"
+#define ERROR 1e-6
+#include "../simplex.hpp"
+#include <iomanip>
+#include <iostream>
+#include <vector>
+using namespace std;
+
+int main() {
+    cin.tie(nullptr);
+    ios::sync_with_stdio(false);
+
+    int T;
+    cin >> T;
+    while (T--) {
+        int N, M;
+        cin >> N >> M;
+        vector A(N, vector<double>(M));
+        for (auto &a : A) {
+            for (auto &x : a) cin >> x;
+        };
+
+        // Minimize v = v_pos - v_neg over Bob's distribution q:
+        // A q <= v, sum(q) = 1, q >= 0.
+        for (auto &a : A) {
+            a.push_back(-1);
+            a.push_back(1);
+        }
+
+        A.push_back({});
+        for (int t = 0; t < M; ++t) A.back().push_back(1);
+        A.back().push_back(0);
+        A.back().push_back(0);
+
+        A.push_back({});
+        for (int t = 0; t < M; ++t) A.back().push_back(-1);
+        A.back().push_back(0);
+        A.back().push_back(0);
+
+        vector<double> B(A.size() - 2, 0);
+        B.push_back(1);
+        B.push_back(-1);
+
+        vector<double> C(A.front().size());
+        C.at(C.size() - 2) = -1;
+        C.back() = 1;
+
+        Simplex<double> simplex{A, B, C};
+        cout << fixed << setprecision(15) << -simplex.ans << '\n';
+    }
+}