cpp: add «1971. Find if Path Exists in Graph»

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

cpp/find-if-path-exists-in-graph.cpp

@@ -0,0 +1,35 @@
+#include <vector>
+
+struct Solution {
+    using edges_t = std::vector<std::vector<int>>;
+
+    bool validPath(int n, const edges_t &edges, int source, int destination) {
+        std::vector<bool> visited(n);
+        visited[source] = true;
+
+        bool changed;
+        do {
+            changed = iterate(edges, visited);
+        } while (changed && !visited[destination]);
+
+        return visited[destination];
+    }
+
+  private:
+    bool iterate(const edges_t &edges, std::vector<bool> &visited) {
+        bool changed = false;
+
+        for (const auto &edge : edges) {
+            auto [u, v] = std::tie(edge[0], edge[1]);
+            if (visited[u] == visited[v]) {
+                continue;
+            }
+
+            visited[u] = true;
+            visited[v] = true;
+            changed = true;
+        }
+
+        return changed;
+    }
+};