feat: C++ exercises

exercises/00_hello_world/main.cpp

@@ -1,11 +1,12 @@
 #include "../exercise.h"
+#include <iostream>
 
 // READ: std streams <https://zh.cppreference.com/w/cpp/io/c/std_streams>
 // READ: 流修饰符 <https://zh.cppreference.com/w/cpp/io/manip>
 // READ: format in cxx20 <https://zh.cppreference.com/w/cpp/utility/format/format>
 
 int main(int argc, char **argv) {
     // TODO: 在控制台输出 "Hello, InfiniTensor!" 并换行
-    std::cout : "Hello, InfiniTensor!" + std::endl;
+    std::cout << "Hello, InfiniTensor!" << std::endl;
     return 0;
 }

exercises/01_variable&add/main.cpp

@@ -1,10 +1,12 @@
 #include "../exercise.h"
+#include <iostream>
 
 // READ: 运算符 <https://zh.cppreference.com/w/cpp/language/expressions#.E8.BF.90.E7.AE.97.E7.AC.A6>
 
 int main(int argc, char **argv) {
     // TODO: 补全变量定义并打印加法运算
-    // x ?
+    int x = 5;
+    // std::cin >> x;
     std::cout << x << " + " << x << " = " << x + x << std::endl;
     return 0;
 }

exercises/02_function/main.cpp

@@ -1,10 +1,12 @@
 #include "../exercise.h"
+#include <iostream>
 
 // READ: 声明 <https://zh.cppreference.com/w/cpp/language/declarations>
 // NOTICE: cppreference 中的示例中指出了复杂声明的解读法，建议认真阅读。
 // NOTICE: 补充由内而外读法的机翻解释 <https://learn.microsoft.com/zh-cn/cpp/c-language/interpreting-more-complex-declarators?view=msvc-170>
 
 // TODO: 在这里声明函数
+int add(int a, int b);
 
 int main(int argc, char **argv) {
     ASSERT(add(123, 456) == 123 + 456, "add(123, 456) should be 123 + 456");
@@ -16,4 +18,5 @@ int main(int argc, char **argv) {
 
 int add(int a, int b) {
     // TODO: 补全函数定义，但不要移动代码行
+    return a + b;
 }

exercises/03_argument&parameter/main.cpp

@@ -8,19 +8,19 @@ void func(int);
 // TODO: 为下列 ASSERT 填写正确的值
 int main(int argc, char **argv) {
     auto arg = 99;
-    ASSERT(arg == ?, "arg should be ?");
+    ASSERT(arg == 99, "arg should be ?");
     std::cout << "befor func call: " << arg << std::endl;
     func(arg);
-    ASSERT(arg == ?, "arg should be ?");
+    ASSERT(arg == 99, "arg should be ?");
     std::cout << "after func call: " << arg << std::endl;
     return 0;
 }
 
 // TODO: 为下列 ASSERT 填写正确的值
 void func(int param) {
-    ASSERT(param == ?, "param should be ?");
+    ASSERT(param == 99, "param should be ?");
     std::cout << "befor add: " << param << std::endl;
     param += 1;
-    ASSERT(param == ?, "param should be ?");
+    ASSERT(param == 100, "param should be ?");
     std::cout << "after add: " << param << std::endl;
 }

exercises/04_static/main.cpp

@@ -10,10 +10,10 @@ static int func(int param) {
 
 int main(int argc, char **argv) {
     // TODO: 将下列 `?` 替换为正确的数字
-    ASSERT(func(5) == ?, "static variable value incorrect");
-    ASSERT(func(4) == ?, "static variable value incorrect");
-    ASSERT(func(3) == ?, "static variable value incorrect");
-    ASSERT(func(2) == ?, "static variable value incorrect");
-    ASSERT(func(1) == ?, "static variable value incorrect");
+    ASSERT(func(5) == 5, "static variable value incorrect");
+    ASSERT(func(4) == 6, "static variable value incorrect");
+    ASSERT(func(3) == 7, "static variable value incorrect");
+    ASSERT(func(2) == 8, "static variable value incorrect");
+    ASSERT(func(1) == 9, "static variable value incorrect");
     return 0;
 }

exercises/05_constexpr/main.cpp

@@ -1,4 +1,23 @@
 #include "../exercise.h"
+#include <iostream>
+
+/*
+// Performance improved version: Reduce time complexity from O(2^n) to O(n)
+constexpr unsigned long long fibonacci2(int n) {
+    int i = 2;
+    int f_1 = 1;
+    int f_2 = 0;
+    int f = 0;
+    do {
+        f = f_1 + f_2;
+        f_2 = f_1;
+        f_1 = f;
+        i++;
+    } while (i <= n);
+    unsigned long long result = f;
+    return result;
+}
+*/
 
 constexpr unsigned long long fibonacci(int i) {
     switch (i) {
@@ -15,12 +34,15 @@ int main(int argc, char **argv) {
     constexpr auto FIB20 = fibonacci(20);
     ASSERT(FIB20 == 6765, "fibonacci(20) should be 6765");
     std::cout << "fibonacci(20) = " << FIB20 << std::endl;
+    // std::cout << "fibonacci(20) = " << fibonacci(20) << std::endl;
+    // std::cout << "fibonacci2(20) = " << fibonacci2(20) << std::endl;
 
     // TODO: 观察错误信息，修改一处，使代码编译运行
     // PS: 编译运行，但是不一定能算出结果……
-    constexpr auto ANS_N = 90;
-    constexpr auto ANS = fibonacci(ANS_N);
+    constexpr auto ANS_N = 10;
+    auto ANS = fibonacci(ANS_N);
     std::cout << "fibonacci(" << ANS_N << ") = " << ANS << std::endl;
+    // std::cout << "fibonacci2(90) = " << fibonacci2(90) << std::endl;
 
     return 0;
 }

exercises/06_array/main.cpp

@@ -11,13 +11,13 @@ unsigned long long fibonacci(int i) {
             return 1;
         default:
             // TODO: 补全三目表达式缺失的部分
-            return <condition> ? <cache> : (arr[i] = fibonacci(i - 1) + fibonacci(i - 2));
+            return (arr[i]) != 0 ? arr[i] : (arr[i] = fibonacci(i - 1) + fibonacci(i - 2));
     }
 }
 
 int main(int argc, char **argv) {
     // TODO: 为此 ASSERT 填写正确的值
-    ASSERT(sizeof(arr) == ?, "sizeof array is size of all its elements");
+    ASSERT(sizeof(arr) == 90 * sizeof(unsigned long long), "sizeof array is size of all its elements");
     // ---- 不要修改以下代码 ----
     ASSERT(fibonacci(2) == 1, "fibonacci(2) should be 1");
     ASSERT(fibonacci(20) == 6765, "fibonacci(20) should be 6765");

exercises/07_loop/main.cpp

@@ -1,13 +1,21 @@
 #include "../exercise.h"
+#include <iostream>
 
 // TODO: 改正函数实现，实现正确的缓存优化斐波那契计算
 // THINk: 这个函数是一个纯函数（pure function）吗？
 // READ: 纯函数 <https://zh.wikipedia.org/wiki/%E7%BA%AF%E5%87%BD%E6%95%B0>
 static unsigned long long fibonacci(int i) {
     // TODO: 为缓存设置正确的初始值
     static unsigned long long cache[96], cached;
+
+    if (cached == 0) {
+        cache[0] = 0ULL;
+        cache[1] = 1ULL;
+        cached = 2;
+    }
     // TODO: 设置正确的循环条件
-    for (; false; ++cached) {
+    // static_cast<unsigned>(i) is to resolve the warning different signedness: ‘long long unsigned int’ and ‘int’
+    for (; cached <= static_cast<unsigned>(i); ++cached) {
         cache[cached] = cache[cached - 1] + cache[cached - 2];
     }
     return cache[i];

exercises/08_pointer/main.cpp

@@ -3,8 +3,15 @@
 // READ: 数组向指针退化 <https://zh.cppreference.com/w/cpp/language/array#%E6%95%B0%E7%BB%84%E5%88%B0%E6%8C%87%E9%92%88%E7%9A%84%E9%80%80%E5%8C%96>
 bool is_fibonacci(int *ptr, int len, int stride) {
     ASSERT(len >= 3, "`len` should be at least 3");
+    if (stride <= 0) return false;    // basic guard
     // TODO: 编写代码判断从 ptr 开始，每 stride 个元素取 1 个元素，组成长度为 n 的数列是否满足
     // arr[i + 2] = arr[i] + arr[i + 1]
+    for (int k = 0; k <= len - 3; ++k) {
+        int a0 = ptr[k *stride];
+        int a1 = ptr[(k + 1) * stride];
+        int a2 = ptr[(k + 2) * stride];
+        if (a2 != a0 + a1) return false;
+    }
     return true;
 }
 

exercises/09_enum&union/main.cpp

@@ -37,6 +37,11 @@ ColorEnum convert_by_pun(Color c) {
 
     TypePun pun;
     // TODO: 补全类型双关转换
+    pun.c = c;
+    // Well-defined conversion: Color(enum class,int) -> int -> unsigned char -> ColorEnum
+    pun.e = static_cast<ColorEnum>(
+                static_cast<unsigned char>(
+                    static_cast<std::underlying_type_t<Color>>(pun.c)));
 
     return pun.e;
 }

exercises/10_trivial/main.cpp

@@ -1,4 +1,5 @@
 #include "../exercise.h"
+#include <iostream>
 
 // READ: Trivial type <https://learn.microsoft.com/zh-cn/cpp/cpp/trivial-standard-layout-and-pod-types?view=msvc-170>
 
@@ -8,18 +9,26 @@ struct FibonacciCache {
 };
 
 // TODO: 实现正确的缓存优化斐波那契计算
-static unsigned long long fibonacci(FibonacciCache &cache, int i) {
-    for (; false; ++cached) {
-        cache[cached] = cache[cached - 1] + cache[cached - 2];
+static unsigned long long fibonacci(FibonacciCache &fc, int i) {
+    ASSERT(i >= 0 && i < 16, "i out of range for 16-entry cache")
+    // Guard: initialize F(0)=0, F(1)=1, and cached
+    std::cout << fc.cached << std::endl;
+    ASSERT(fc.cached >= 0 && fc.cached < 16, "fc.cached is out of range for 16 entry cache")
+    if (fc.cached < 2) fc.cached = 2;
+    if (fc.cache[0] != 0) fc.cache[0] = 0ULL;
+    if (fc.cache[1] != 1) fc.cache[1] = 1ULL;
+    // Fill in the Fibonacci variables
+    for (; fc.cached <= i; ++fc.cached) {
+        fc.cache[fc.cached] = fc.cache[fc.cached - 1] + fc.cache[fc.cached - 2];
     }
-    return cache.cache[i];
+    return fc.cache[i];
 }
 
 int main(int argc, char **argv) {
     // TODO: 初始化缓存结构体，使计算正确
     // NOTICE: C/C++ 中，读取未初始化的变量（包括结构体变量）是未定义行为
     // READ: 初始化的各种写法 <https://zh.cppreference.com/w/cpp/language/initialization>
-    FibonacciCache fib;
+    FibonacciCache fib{{0ULL, 1ULL}, 2};
     ASSERT(fibonacci(fib, 10) == 55, "fibonacci(10) should be 55");
     std::cout << "fibonacci(10) = " << fibonacci(fib, 10) << std::endl;
     return 0;

exercises/11_method/main.cpp

@@ -1,12 +1,21 @@
 #include "../exercise.h"
+#include <iostream>
 
 struct Fibonacci {
     unsigned long long cache[128];
     int cached;
 
     // TODO: 实现正确的缓存优化斐波那契计算
     unsigned long long get(int i) {
-        for (; false; ++cached) {
+        ASSERT(i >= 0 && i < 128, "i out of range for 128-entry cache");
+
+        // Guard: initialize F(0), F(1) and minimum index:
+        if (cached < 2 || cached >= 128) cached = 2;
+        if (cache[0] != 0) cache[0] = 0ULL;
+        if (cache[1] != 1) cache[1] = 1ULL;
+
+        // calculate Fibonacci
+        for (; cached <= i; ++cached) {
             cache[cached] = cache[cached - 1] + cache[cached - 2];
         }
         return cache[i];
@@ -15,7 +24,7 @@ struct Fibonacci {
 
 int main(int argc, char **argv) {
     // TODO: 初始化缓存结构体，使计算正确
-    Fibonacci fib;
+    Fibonacci fib{{0, 1}, 2};
     ASSERT(fib.get(10) == 55, "fibonacci(10) should be 55");
     std::cout << "fibonacci(10) = " << fib.get(10) << std::endl;
     return 0;

exercises/12_method_const/main.cpp

@@ -1,11 +1,13 @@
 #include "../exercise.h"
+#include <iostream>
 
 // READ: 有 cv 限定符的成员函数 <https://zh.cppreference.com/w/cpp/language/member_functions>
 
 struct Fibonacci {
     int numbers[11];
     // TODO: 修改方法签名和实现，使测试通过
-    int get(int i) {
+    constexpr int get(int i) const{
+        return numbers[i];
     }
 };
 

exercises/13_class/main.cpp

@@ -14,11 +14,15 @@ class Fibonacci {
 
 public:
     // TODO: 实现构造器
-    // Fibonacci()
+    Fibonacci() : cache{0, 1}, cached(2) {}
 
     // TODO: 实现正确的缓存优化斐波那契计算
     size_t get(int i) {
-        for (; false; ++cached) {
+        // Guard: initialize cache[0] + cache[1] and cached >= 2
+        cache[0] = 0ULL;
+        cache[1] = 1ULL;
+        if (cached < 2) cached = 2;
+        for (; cached <= i; ++cached) {
             cache[cached] = cache[cached - 1] + cache[cached - 2];
         }
         return cache[i];
@@ -28,7 +32,7 @@ class Fibonacci {
 int main(int argc, char **argv) {
     // 现在类型拥有无参构造器，声明时会直接调用。
     // 这个写法不再是未定义行为了。
-    Fibonacci fib;
+    Fibonacci fib{};
     ASSERT(fib.get(10) == 55, "fibonacci(10) should be 55");
     std::cout << "fibonacci(10) = " << fib.get(10) << std::endl;
     return 0;

exercises/14_class_destruct/main.cpp

@@ -1,4 +1,5 @@
 #include "../exercise.h"
+#include <iostream>
 
 // READ: 析构函数 <https://zh.cppreference.com/w/cpp/language/destructor>
 // READ: RAII <https://learn.microsoft.com/zh-cn/cpp/cpp/object-lifetime-and-resource-management-modern-cpp?view=msvc-170>
@@ -11,14 +12,20 @@ class DynFibonacci {
 
 public:
     // TODO: 实现动态设置容量的构造器
-    DynFibonacci(int capacity): cache(new ?), cached(?) {}
+    DynFibonacci(int capacity)
+        : cache(new size_t[capacity]{}), cached(2) {
+            cache[0] = 0;
+            cache[1] = 1;
+        }
 
     // TODO: 实现析构器，释放缓存空间
-    ~DynFibonacci();
+    ~DynFibonacci() {
+        delete[] cache;
+    };
 
     // TODO: 实现正确的缓存优化斐波那契计算
     size_t get(int i) {
-        for (; false; ++cached) {
+        for (; cached <= i; ++cached) {
             cache[cached] = cache[cached - 1] + cache[cached - 2];
         }
         return cache[i];

exercises/15_class_clone/main.cpp

@@ -1,4 +1,6 @@
 #include "../exercise.h"
+#include <iostream>
+#include <algorithm>
 
 // READ: 复制构造函数 <https://zh.cppreference.com/w/cpp/language/copy_constructor>
 // READ: 函数定义（显式弃置）<https://zh.cppreference.com/w/cpp/language/function>
@@ -10,17 +12,26 @@ class DynFibonacci {
 
 public:
     // TODO: 实现动态设置容量的构造器
-    DynFibonacci(int capacity): cache(new ?), cached(?) {}
+    DynFibonacci(int capacity): cache(new size_t[capacity]{}), cached(2) {
+        ASSERT(capacity >= 2, "capacity must be at least 2");
+        cache[0] = 0; cache[1] = 1; cached = 2;
+    }
 
     // TODO: 实现复制构造器
-    DynFibonacci(DynFibonacci const &) = delete;
+    DynFibonacci(DynFibonacci const &other)
+        : cache(new size_t[other.cached + 1]{}), cached(other.cached) {
+            std::copy(other.cache, other.cache + other.cached + 1, cache);
+        }
+
 
     // TODO: 实现析构器，释放缓存空间
-    ~DynFibonacci();
+    ~DynFibonacci() {
+        delete[] cache;
+    }
 
     // TODO: 实现正确的缓存优化斐波那契计算
     size_t get(int i) {
-        for (; false; ++cached) {
+        for (; cached <= i; ++cached) {
             cache[cached] = cache[cached - 1] + cache[cached - 2];
         }
         return cache[i];
@@ -40,6 +51,7 @@ class DynFibonacci {
 
 int main(int argc, char **argv) {
     DynFibonacci fib(12);
+    // std::cout << fib.get(10) << std::endl;
     ASSERT(fib.get(10) == 55, "fibonacci(10) should be 55");
     DynFibonacci const fib_ = fib;
     ASSERT(fib_.get(10) == fib.get(10), "Object cloned");