Solved: 07 - Loops

Added a contract precondition to factorial

modules/02_control_flow/include/loops.hpp

@@ -5,7 +5,8 @@
 namespace control_flow {
 
 [[nodiscard]] auto sum_range(int from, int to) -> int;
-[[nodiscard]] auto factorial(int n) -> long long;
+// ReSharper disable once CppConstParameterInDeclaration
+[[nodiscard]] auto factorial(const int n) -> long long pre(n >= 0);
 [[nodiscard]] auto count_occurrences(const std::vector<int>& data, int target) -> int;
 [[nodiscard]] auto first_index_of(const std::vector<int>& data, int target) -> int;
 

modules/02_control_flow/src/loops.cpp

@@ -1,26 +1,41 @@
 #include "loops.hpp"
 
+#include <algorithm>
+#include <ranges>
+
 namespace control_flow {
 
-auto sum_range(int from, int to) -> int {
-    (void)from; (void)to;
-    return 0;
+auto sum_range(const int from, const int to) -> int {
+    return std::ranges::fold_left(
+        std::views::iota(from, to + 1), // End-exclusive
+        0,
+        [](const int acc, const int x) { return acc + x; }
+    );
 }
 
-auto factorial(int n) -> long long {
-    (void)n;
-    return 1;
+auto factorial(const int n) -> long long
+    pre(n >= 0)
+{
+    if (n == 0 || n == 1) return 1;
+    return std::ranges::fold_left(
+        std::views::iota(2, n + 1), // End-exclusive
+        1LL,
+        [](const long long acc, const int x) { return acc * x; }
+    );
 }
 
-auto count_occurrences(const std::vector<int>& data, int target) -> int {
-    (void)data; (void)target;
-    return 0;
+auto count_occurrences(const std::vector<int>& data, const int target) -> int {
+    int count = 0;
+    std::ranges::for_each(data, [target, &count](const int x) {
+        if (x == target) ++count;
+    });
+    return count;
 }
 
-auto first_index_of(const std::vector<int>& data, int target) -> int {
-    // TODO: Return index or -1 if not found
-    (void)data; (void)target;
-    return -1;
+auto first_index_of(const std::vector<int>& data, const int target) -> int {
+    const auto it = std::ranges::find(data, target);
+    if (it == data.end()) return -1;
+    return static_cast<int>(std::distance(data.begin(), it));
 }
 
 }  // namespace control_flow

modules/02_control_flow/test/loops_test.cpp

@@ -9,6 +9,12 @@ TEST(Loops, SumRange) {
 TEST(Loops, Factorial) {
     EXPECT_EQ(control_flow::factorial(0), 1);
     EXPECT_EQ(control_flow::factorial(5), 120);
+    // Breach of contract
+    EXPECT_DEATH(
+    {
+        (void)control_flow::factorial(-1);
+    },
+    "contract violation");
 }
 
 TEST(Loops, CountOccurrences) {