From 96254947699986c59f0dc63d69fd4b76bd3ed43e Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Mon, 6 Jul 2026 19:08:08 +0200
Subject: Initial commit

---
 15_advanced_graph_problems/nearest_shops_3303.cpp | 55 +++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 15_advanced_graph_problems/nearest_shops_3303.cpp

(limited to '15_advanced_graph_problems/nearest_shops_3303.cpp')

diff --git a/15_advanced_graph_problems/nearest_shops_3303.cpp b/15_advanced_graph_problems/nearest_shops_3303.cpp
new file mode 100644
index 0000000..ce62098
--- /dev/null
+++ b/15_advanced_graph_problems/nearest_shops_3303.cpp
@@ -0,0 +1,55 @@
+#include <algorithm>
+#include <iostream>
+#include <queue>
+#include <tuple>
+#include <vector>
+
+// The difficult part is finding for every city with an anime shop the
+// closest other city with a shop. We do this via a "double BFS", where
+// we reach each node twice from two different sources.
+
+struct V { int v1; int s1; int v2; int s2; };
+
+int main() {
+	constexpr int max{99999999};
+	int n, m, k, x, y;
+	std::queue<std::tuple<int, int, int>> q;
+	std::cin >> n >> m >> k;
+	std::vector<V> v(n, {max, -1, max, -1});
+	for (int i = 0; i < k; i++) {
+		std::cin >> x;
+		v[x-1] = {0, x-1, max, -1};
+		q.push({x-1, 0, x-1});
+	}
+	std::vector<std::vector<int>> a(n);
+	for (int i = 0; i < m; i++) {
+		std::cin >> x >> y;
+		a[x-1].push_back(y-1);
+		a[y-1].push_back(x-1);
+	}
+
+	while (!q.empty()) {
+		auto [u, w, s] = q.front();
+		q.pop();
+		for (auto z : a[u]) {
+			if (z == s) continue;
+			auto& [v1, s1, v2, s2] = v[z];
+			if (v1 > w+1) {
+				v1 = w+1;
+				s1 = s;
+				q.push({z, w+1, s});
+			} else if (s1 != s && v2 > w+1) {
+				v2 = w+1;
+				s2 = s;
+				q.push({z, w+1, s});
+			}
+		}
+	}
+
+	for (int i = 0; i < n; i++) {
+		auto [x, s, y, _] = v[i];
+		auto w = s == i ? y : x;
+		std::cout << (w == max ? -1 : w) << " ";
+	}
+	std::cout << "\n";
+}
-- 
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