Add unit test for n-queens (#273)

* Add unit test for n-queens
* Update readme with white check

Co-authored-by: Alex Johnson <alxmjo@gmail.com>

C++/CMakeLists.txt

@@ -19,6 +19,15 @@ add_library(test_runner STATIC
 # Algorithms
 # ============================================================================
 
+# -------------------
+# Backtracking
+# -------------------
+
+# N-Queens
+add_executable(n_queens
+        test/algorithm/backtracking/n_queens.cpp)
+target_link_libraries(n_queens test_runner)
+
 # -------------------
 # Dynamic programming
 # -------------------

C++/README.md

@@ -11,8 +11,8 @@ Implementing well-known (and some rare) **algorithms and data structures in C++*
 ### Algorithms
 
 * Backtracking
-  * [N-Queens](include/algorithm/backtracking/n_queens.hpp)
-  
+  * [N-Queens](include/algorithms/backtracking/n_queens.hpp) :white_check_mark:
+
 * Dynamic programming
   * [0-1 knapsack](include/algorithm/dynamic_programming/0_1_knapsack.hpp) :white_check_mark:
   * [Coin change](include/algorithm/dynamic_programming/coin_change.hpp) :white_check_mark:

C++/test/algorithm/backtracking/n_queens.cpp

@@ -0,0 +1,59 @@
+#include "third_party/catch.hpp"
+#include "algorithm/backtracking/n_queens.hpp"
+
+TEST_CASE("Base cases", "[backtracking][n_queens]") {
+    // N = 0 (cannot place)
+    NQueensSolver b0(0);
+    REQUIRE(b0.can_place_queens() == false);
+
+    // N = 1 (can place)
+    NQueensSolver b1(1);
+    REQUIRE(b1.can_place_queens() == true);
+    REQUIRE(b1.num_solutions() == 1);
+    Board b1_sln {{true}};
+    REQUIRE(b1.get_solution() == b1_sln);
+    std::vector<Board> b1_slns {{{true}}};
+    REQUIRE(b1.get_solutions() == b1_slns);
+}
+
+TEST_CASE("Unplaceable cases", "[backtracking][n_queens]") {
+    // N = 2
+    NQueensSolver b2(2);
+    REQUIRE(b2.can_place_queens() == false);
+
+    // N = 3
+    NQueensSolver b3(3);
+    REQUIRE(b3.can_place_queens() == false);
+}
+
+TEST_CASE("Placeable cases", "[backtracking][n_queens]") {
+    // N = 4
+    NQueensSolver b4(4);
+    REQUIRE(b4.can_place_queens() == true);
+    REQUIRE(b4.num_solutions() == 2);
+    Board b4_sln1 {
+        {false, true, false, false},
+        {false, false, false, true},
+        {true, false, false, false},
+        {false, false, true, false}
+    };
+    Board b4_sln2 {
+        {false, false, true, false},
+        {true, false, false, false},
+        {false, false, false, true},
+        {false, true, false, false}
+    };
+    using Catch::Matchers::VectorContains;
+    REQUIRE_THAT(b4.get_solutions(), VectorContains(b4_sln1));
+    REQUIRE_THAT(b4.get_solutions(), VectorContains(b4_sln2));
+
+    // N = 9
+    NQueensSolver b9(9);
+    REQUIRE(b9.can_place_queens() == true);
+    REQUIRE(b9.num_solutions() == 352);
+
+    // N = 11
+    NQueensSolver b11(11);
+    REQUIRE(b11.can_place_queens() == true);
+    REQUIRE(b11.num_solutions() == 2680);
+}