cpp: add «310. Minimum Height Trees»

Signed-off-by: Matej Focko <me@mfocko.xyz>

cpp/minimum-height-trees.cpp

@@ -0,0 +1,80 @@
+#include <algorithm>
+#include <queue>
+#include <vector>
+
+struct Solution {
+    using graph_t = std::vector<std::vector<int>>;
+
+  public:
+    std::vector<int>
+    findMinHeightTrees(int n, const std::vector<std::vector<int>> &edges) {
+        auto g = graph(n, edges);
+
+        std::vector<bool> visited(n);
+        auto nodes = leafs(g, visited);
+        auto d = degrees(g);
+
+        std::vector<int> min_height_roots;
+        while (!nodes.empty()) {
+            auto size = nodes.size();
+            min_height_roots.clear();
+
+            for (auto i = 0u; i < size; ++i) {
+                auto u = nodes.front();
+                nodes.pop();
+
+                min_height_roots.push_back(u);
+                for (auto v : g[u]) {
+                    if (visited[v]) {
+                        continue;
+                    }
+
+                    if ((--d[v]) == 1) {
+                        visited[v] = true;
+                        nodes.push(v);
+                    }
+                }
+            }
+        }
+
+        return min_height_roots;
+    }
+
+  private:
+    graph_t graph(int n, const graph_t &edges) {
+        graph_t neighbors(n);
+
+        for (const auto &e : edges) {
+            auto [u, v] = std::make_pair(e[0], e[1]);
+            neighbors[u].push_back(v);
+            neighbors[v].push_back(u);
+        }
+
+        return neighbors;
+    }
+
+    std::queue<int> leafs(const graph_t &g, std::vector<bool> &visited) {
+        std::queue<int> nodes;
+
+        for (auto u = 0u; u < g.size(); ++u) {
+            if (g[u].size() >= 2) {
+                continue;
+            }
+
+            visited[u] = true;
+            nodes.push(u);
+        }
+
+        return nodes;
+    }
+
+    std::vector<int> degrees(const graph_t &g) {
+        std::vector<int> d(g.size());
+
+        for (auto i = 0u; i < g.size(); ++i) {
+            d[i] = g[i].size();
+        }
+
+        return d;
+    }
+};