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1 files changed, 55 insertions, 0 deletions

diff --git a/15_advanced_graph_problems/nearest_shops_3303.cpp b/15_advanced_graph_problems/nearest_shops_3303.cpp
new file mode 100644
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+++ b/15_advanced_graph_problems/nearest_shops_3303.cpp
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+#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";
+}