Cheapest Flights Within K Stops

CMakeLists.txt

@@ -75,6 +75,7 @@ add_task(can-place-flowers)
 add_task(candy)
 add_task(capacity-to-ship-packages-within-d-days)
 add_task(champagne-tower)
+add_task(cheapest-flights-within-k-stops)
 add_task(check-completeness-of-a-binary-tree)
 add_task(check-if-array-is-sorted-and-rotated)
 add_task(check-if-it-is-a-straight-line)

solutions/cheapest-flights-within-k-stops/CMakeLists.txt

@@ -0,0 +1 @@
+add_catch(test_cheapest_flights_within_k_stops test.cpp)

solutions/cheapest-flights-within-k-stops/solution.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <algorithm>
+#include <climits>
+#include <queue>
+#include <vector>
+
+class Solution {
+public:
+  static int findCheapestPrice(int n,
+                               const std::vector<std::vector<int>> &flights,
+                               int src, int dst, int k) {
+    std::vector<std::vector<std::pair<int, int>>> graph(n);
+    for (const auto &edge : flights) {
+      const auto from = edge[0], to = edge[1], price = edge[2];
+      graph[from].push_back({to, price});
+    }
+
+    std::vector<int> distances(n, INT_MAX);
+    distances[src] = 0;
+
+    std::queue<std::pair<int, int>> queue;
+    queue.push({src, 0});
+
+    for (int stops = 0; !queue.empty() && stops <= k; ++stops) {
+      for (int sz = queue.size(); sz; --sz) {
+        const auto [u, distance] = queue.front();
+        queue.pop();
+
+        for (const auto &[v, w] : graph[u]) {
+          if (distances[v] > distance + w) {
+            distances[v] = distance + w;
+            queue.push({v, distance + w});
+          }
+        }
+      }
+    }
+
+    return distances[dst] == INT_MAX ? -1 : distances[dst];
+  }
+};

solutions/cheapest-flights-within-k-stops/test.cpp

@@ -0,0 +1,27 @@
+#include <catch.hpp>
+
+#include <solution.hpp>
+
+TEST_CASE("Simple") {
+  {
+    int n = 4;
+    std::vector<std::vector<int>> flights{
+        {0, 1, 100}, {1, 2, 100}, {2, 0, 100}, {1, 3, 600}, {2, 3, 200}};
+    int src = 0, dst = 3, k = 1;
+    REQUIRE(700 == Solution::findCheapestPrice(n, flights, src, dst, k));
+  }
+  {
+    int n = 3;
+    std::vector<std::vector<int>> flights{
+        {0, 1, 100}, {1, 2, 100}, {0, 2, 500}};
+    int src = 0, dst = 2, k = 1;
+    REQUIRE(200 == Solution::findCheapestPrice(n, flights, src, dst, k));
+  }
+  {
+    int n = 3;
+    std::vector<std::vector<int>> flights{
+        {0, 1, 100}, {1, 2, 100}, {0, 2, 500}};
+    int src = 0, dst = 2, k = 0;
+    REQUIRE(500 == Solution::findCheapestPrice(n, flights, src, dst, k));
+  }
+}