(PR #204) update c code and doc for time_complexity

codes/c/chapter_array_and_linkedlist/array.c

@@ -0,0 +1,112 @@
+/*
+ * File: array.c
+ * Created Time: 2022-12-20
+ * Author: MolDuM (moldum@163.com)
+ */
+
+#include "../include/include.h"
+
+/* 随机返回一个数组元素 */
+int randomAccess(int* nums, int size) {
+    // 在区间 [0, size) 中随机抽取一个数字
+    int randomIndex = rand() % size;
+    // 获取并返回随机元素
+    int randomNum = nums[randomIndex];
+    return randomNum;
+}
+
+/* 扩展数组长度 */
+int* extend(int* nums, int size, int enlarge) {
+    // 初始化一个扩展长度后的数组
+    int* res = (int *)malloc(sizeof(int) * (size + enlarge));
+    // 将原数组中的所有元素复制到新数组
+    for (int i = 0; i < size; i++) {
+        res[i] = nums[i];
+    }
+    // 初始化扩展后的空间
+    for (int i = size; i < size + enlarge; i++) {
+        res[i] = 0;
+    }
+    // 返回扩展后的新数组
+    return res;
+}
+
+/* 在数组的索引 index 处插入元素 num */
+void insert(int* nums, int size, int num, int index) {
+    // 把索引 index 以及之后的所有元素向后移动一位
+    for (int i = size - 1; i > index; i--) {
+        nums[i] = nums[i - 1];
+    }
+    // 将 num 赋给 index 处元素
+    nums[index] = num;
+}
+
+/* 删除索引 index 处元素 */
+void removeItem(int* nums, int size, int index) {
+    // 把索引 index 之后的所有元素向前移动一位
+    for (int i = index; i < size - 1; i++) {
+        nums[i] = nums[i + 1];
+    }
+}
+
+/* 遍历数组 */
+void traverse(int* nums, int size) {
+    int count = 0;
+    // 通过索引遍历数组
+    for (int i = 0; i < size; i++) {
+        count++;
+    }
+}
+
+/* 在数组中查找指定元素 */
+int find(int* nums, int size, int target) {
+    for (int i = 0; i < size; i++) {
+        if (nums[i] == target)
+            return i;
+    }
+    return -1;
+}
+
+
+/* Driver Code */
+int main() {
+    /* 初始化数组 */
+    int size = 5;
+    int arr[5];
+    printf("数组 arr = ");
+    printArray(arr, size);
+
+    int nums[5] = { 1, 3, 2, 5, 4 };
+    printf("数组 nums = ");
+    printArray(nums, size);
+    
+    /* 随机访问 */
+    int randomNum = randomAccess(nums, size);
+    printf("在 nums 中获取随机元素 %d", randomNum);
+    
+    /* 长度扩展 */
+    int enlarge = 3;
+    int* res = extend(nums, size, enlarge);
+    size += enlarge;
+    printf("将数组长度扩展至 8 ，得到 nums = ");
+    printArray(res, size);
+    
+    /* 插入元素 */
+    insert(res, size, 6, 3);
+    printf("在索引 3 处插入数字 6 ，得到 nums = ");
+    printArray(res, size);
+
+    /* 删除元素 */
+    removeItem(res, size, 2);
+    printf("删除索引 2 处的元素，得到 nums = ");
+    printArray(res, size);
+    
+    /* 遍历数组 */
+    traverse(res, size);
+    
+    /* 查找元素 */
+    int index = find(res, size, 3);
+    printf("在 res 中查找元素 3 ，得到索引 = %d\n", index);
+
+    return 0;
+}

codes/c/chapter_computational_complexity/time_complexity.c

@@ -7,33 +7,30 @@
 #include "../include/include.h"
 
 /* 常数阶 */
-int constant(int n) 
-{
+int constant(int n) {
     int count = 0;
     int size = 100000;
     int i = 0;
-    for(int i = 0; i < size; i++){
+    for (int i = 0; i < size; i++) {
         count ++;
     }
     return count;
 }
 
 /* 线性阶 */
-int linear(int n) 
-{
+int linear(int n) {
     int count = 0;
-    for(int i = 0; i < n; i++){
+    for (int i = 0; i < n; i++) {
         count ++;
     }
     return count;
 }
 
 /* 线性阶（遍历数组） */
-int arrayTraversal(int *nums, int n)
-{
+int arrayTraversal(int *nums, int n) {
     int count = 0;
     // 循环次数与数组长度成正比
-    for(int i = 0; i < n; i++){
+    for (int i = 0; i < n; i++) {
         count ++;
     }
     return count;
@@ -44,8 +41,8 @@ int quadratic(int n)
 {
     int count = 0;
     // 循环次数与数组长度成平方关系
-    for(int i = 0; i < n; i++){
-        for(int j = 0; j < n; j++){
+    for (int i = 0; i < n; i++) {
+        for (int j = 0; j < n; j++) {
             count ++;
         }
     }
@@ -53,35 +50,29 @@ int quadratic(int n)
 }
 
 /* 平方阶（冒泡排序） */
-int bubbleSort(int *nums, int n)
-{
+int bubbleSort(int *nums, int n) {
     int count = 0;  // 计数器 
     // 外循环：待排序元素数量为 n-1, n-2, ..., 1
-    for(int i = n - 1; i > 0; i--){
+    for (int i = n - 1; i > 0; i--) {
         // 内循环：冒泡操作
-        for (int j = 0; j < i; j++)
-        {
+        for (int j = 0; j < i; j++) {
             // 交换 nums[j] 与 nums[j + 1]
             int tmp = nums[j];
             nums[j] = nums[j + 1];
             nums[j + 1] = tmp;
             count += 3;  // 元素交换包含 3 个单元操作
         }
-        
     }
     return count;
 }
 
 /* 指数阶（循环实现） */
-int exponential(int n) 
-{
+int exponential(int n) {
     int count = 0;
     int bas = 1;
     // cell 每轮一分为二，形成数列 1, 2, 4, 8, ..., 2^(n-1)
-    for (int i = 0; i < n; i++)
-    {
-        for (int j = 0; j < bas; j++)
-        {
+    for (int i = 0; i < n; i++) {
+        for (int j = 0; j < bas; j++) {
             count++;
         }
         bas *= 2;
@@ -91,18 +82,15 @@ int exponential(int n)
 }
 
 /* 指数阶（递归实现） */
-int expRecur(int n) 
-{
+int expRecur(int n) {
     if (n == 1) return 1;
     return expRecur(n - 1) + expRecur(n - 1) + 1;
 }
 
 /* 对数阶（循环实现） */
-int logarithmic(float n)
-{
+int logarithmic(float n) {
     int count = 0;
-    while (n > 1)
-    {
+    while (n > 1) {
         n = n / 2;
         count++;
     }
@@ -110,40 +98,34 @@ int logarithmic(float n)
 }
 
 /* 对数阶（递归实现） */
-int logRecur(float n)
-{
+int logRecur(float n) {
     if (n <= 1) return 0;
     return logRecur(n / 2) + 1;
 }
 
 /* 线性对数阶 */
-int linearLogRecur(float n)
-{
+int linearLogRecur(float n) {
     if (n <= 1) return 1;
     int count = linearLogRecur(n / 2) +
                 linearLogRecur(n / 2);
-    for (int i = 0; i < n; i++)
-    {
+    for (int i = 0; i < n; i++) {
         count ++;
     }
     return count;
 }
 
 /* 阶乘阶（递归实现） */
-int factorialRecur(int n) 
-{
+int factorialRecur(int n) {
     if (n == 0) return 1;
     int count = 0;
-    for (int i = 0; i < n; i++)
-    {
+    for (int i = 0; i < n; i++) {
         count += factorialRecur(n - 1);
     }
     return count;
 }
 
 /* Driver Code */
-int main(int argc, char *argv[])
- {
+int main(int argc, char *argv[]) {
     // 可以修改 n 运行，体会一下各种复杂度的操作数量变化趋势
     int n = 8;
     printf("输入数据大小 n = %d\n", n);
@@ -160,7 +142,7 @@ int main(int argc, char *argv[])
 
     count = quadratic(n);
     printf("平方阶的计算操作数量 = %d\n", count);
-    for(int i = 0; i < n; i++){
+    for (int i = 0; i < n; i++) {
         nums[i] = n - i;    // [n,n-1,...,2,1]
     }
     count = bubbleSort(nums, n);
@@ -183,7 +165,7 @@ int main(int argc, char *argv[])
     printf("阶乘阶（递归实现）的计算操作数量 = %d\n", count);
 
     // 释放堆区内存
-    if(nums != NULL){
+    if (nums != NULL) {
         free(nums);
         nums = NULL;
     }

codes/c/chapter_computational_complexity/worst_best_time_complexity.c

@@ -7,18 +7,15 @@
 #include "../include/include.h"
 
 /* 生成一个数组，元素为 { 1, 2, ..., n }，顺序被打乱 */
-int *randomNumbers(int n)  
-{
+int *randomNumbers(int n) {
     // 分配堆区内存（创建一维可变长数组：数组中元素数量为n，元素类型为int）
     int *nums = (int *)malloc(n * sizeof(int));
     // 生成数组 nums = { 1, 2, 3, ..., n }
-    for (int i = 0; i < n; i++)
-    {
+    for (int i = 0; i < n; i++) {
         nums[i] = i + 1;
     }
     // 随机打乱数组元素 
-	for (int i = n - 1; i > 0; i--)
-	{
+	for (int i = n - 1; i > 0; i--) {
 		int j = rand() % (i + 1);
 		int temp = nums[i];
 		nums[i] = nums[j];
@@ -28,33 +25,26 @@ int *randomNumbers(int n)
 }
 
 /* 查找数组 nums 中数字 1 所在索引 */
-int findOne(int *nums, int n) 
-{
-    for (int i = 0; i < n; i++)
-    {
+int findOne(int *nums, int n) {
+    for (int i = 0; i < n; i++) {
         if (nums[i] == 1) return i;
     }
     return -1;
 }
 
 /* Driver Code */
-int main(int argc, char *argv[])
-{
+int main(int argc, char *argv[]) {
     // 初始化随机数种子
     srand((unsigned int)time(NULL));
-    for (int i = 0; i < 10; i++)
-    {
+    for (int i = 0; i < 10; i++) {
         int n = 100;
         int *nums = randomNumbers(n);
         int index = findOne(nums, n);
         printf("\n数组 [ 1, 2, ..., n ] 被打乱后 = ");
-        for (int j = 0; j < n; j++)
-        {
-            printf("%d%s", nums[j], (j == n-1)? "" : "," );
-        }
-        printf("\n数字 1 的索引为 %d\n", index);
+        printArray(nums, n);
+        printf("数字 1 的索引为 %d\n", index);
         // 释放堆区内存
-        if(nums != NULL){
+        if (nums != NULL) {
             free(nums);
             nums = NULL;
         }

codes/c/include/PrintUtil.h

@@ -0,0 +1,30 @@
+/*
+ * File: PrintUtil.h
+ * Created Time: 2022-12-21
+ * Author: MolDum (moldum@163.com)
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+// #include "ListNode.h"
+// #include "TreeNode.h"
+
+/**
+ * @brief Print an Array
+ * 
+ * @param arr 
+ * @param n 
+ */
+
+static void printArray(int* arr, int n)
+{
+    printf("[");
+    for (int i = 0; i < n - 1; i++) {
+        printf("%d, ", arr[i]);
+    }
+    printf("%d]\n", arr[n-1]);
+}
+
+

codes/c/include/include.h

@@ -1,4 +1,15 @@
+/*
+ * File: include.h
+ * Created Time: 2022-12-20
+ * Author: MolDuM (moldum@163.com)
+ */
+
 #include <stdio.h>
-#include <stdbool.h>
 #include <stdlib.h>
-#include <time.h>
+#include <string.h>
+#include <stdbool.h>
+#include <time.h>
+
+#include "PrintUtil.h"
+
+

codes/cpp/chapter_stack_and_queue/array_queue.cpp

@@ -50,11 +50,10 @@ public:
     }
 
     /* 出队 */
-    int poll() {
+    void poll() {
         int num = peek();
         // 队头指针向后移动一位，若越过尾部则返回到数组头部
         front = (front + 1) % capacity();
-        return num;
     }
 
     /* 访问队首元素 */
@@ -98,8 +97,8 @@ int main() {
     cout << "队首元素 peek = " << peek << endl;
     
     /* 元素出队 */
-    int poll = queue->poll();
-    cout << "出队元素 poll = " << poll << "，出队后 queue = ";
+    queue->poll();
+    cout << "出队元素 poll = " << peek << "，出队后 queue = ";
     PrintUtil::printVector(queue->toVector());
 
     /* 获取队列的长度 */

codes/cpp/chapter_stack_and_queue/array_stack.cpp

@@ -28,10 +28,9 @@ public:
     }
 
     /* 出栈 */
-    int pop() {
+    void pop() {
         int oldTop = top();
         stack.pop_back();
-        return oldTop;
     }
 
     /* 访问栈顶元素 */
@@ -67,8 +66,8 @@ int main() {
     cout << "栈顶元素 top = " << top << endl;
 
     /* 元素出栈 */
-    int pop = stack->pop();
-    cout << "出栈元素 pop = " << pop << "，出栈后 stack = ";
+    stack->pop();
+    cout << "出栈元素 pop = " << top << "，出栈后 stack = ";
     PrintUtil::printVector(stack->toVector());
 
     /* 获取栈的长度 */

codes/cpp/chapter_stack_and_queue/linkedlist_queue.cpp

@@ -47,7 +47,7 @@ public:
     }
 
     /* 出队 */
-    int poll() {
+    void poll() {
         int num = peek();
         // 删除头结点
         ListNode *tmp = front;
@@ -55,7 +55,6 @@ public:
         // 释放内存
         delete tmp; 
         queSize--;
-        return num;
     }
 
     /* 访问队首元素 */
@@ -97,8 +96,8 @@ int main() {
     cout << "队首元素 peek = " << peek << endl;
 
     /* 元素出队 */
-    int poll = queue->poll();
-    cout << "出队元素 poll = " << poll << "，出队后 queue = ";
+    queue->poll();
+    cout << "出队元素 poll = " << peek << "，出队后 queue = ";
     PrintUtil::printVector(queue->toVector());
 
     /* 获取队列的长度 */

codes/cpp/chapter_stack_and_queue/linkedlist_stack.cpp

@@ -37,14 +37,13 @@ public:
     }
 
     /* 出栈 */
-    int pop() {
+    void pop() {
         int num = top();
         ListNode *tmp = stackTop;
         stackTop = stackTop->next;
         // 释放内存
         delete tmp;
         stkSize--;
-        return num;
     }
 
     /* 访问栈顶元素 */
@@ -86,8 +85,8 @@ int main() {
     cout << "栈顶元素 top = " << top << endl;
 
     /* 元素出栈 */
-    int pop = stack->pop();
-    cout << "出栈元素 pop = " << pop << "，出栈后 stack = ";
+    stack->pop();
+    cout << "出栈元素 pop = " << top << "，出栈后 stack = ";
     PrintUtil::printVector(stack->toVector());
 
     /* 获取栈的长度 */

codes/swift/Package.swift

@@ -8,11 +8,13 @@ let package = Package(
         .executable(name: "time_complexity", targets: ["time_complexity"]),
         .executable(name: "worst_best_time_complexity", targets: ["worst_best_time_complexity"]),
         .executable(name: "space_complexity", targets: ["space_complexity"]),
+        .executable(name: "leetcode_two_sum", targets: ["leetcode_two_sum"]),
     ],
     targets: [
         .target(name: "utils", path: "utils"),
         .executableTarget(name: "time_complexity", path: "chapter_computational_complexity", sources: ["time_complexity.swift"]),
         .executableTarget(name: "worst_best_time_complexity", path: "chapter_computational_complexity", sources: ["worst_best_time_complexity.swift"]),
         .executableTarget(name: "space_complexity", dependencies: ["utils"], path: "chapter_computational_complexity", sources: ["space_complexity.swift"]),
+        .executableTarget(name: "leetcode_two_sum", path: "chapter_computational_complexity", sources: ["leetcode_two_sum.swift"]),
     ]
 )

codes/swift/chapter_computational_complexity/leetcode_two_sum.swift

@@ -0,0 +1,46 @@
+/*
+ * File: leetcode_two_sum.swift
+ * Created Time: 2023-01-03
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+func twoSumBruteForce(nums: [Int], target: Int) -> [Int] {
+    // 两层循环，时间复杂度 O(n^2)
+    for i in nums.indices.dropLast() {
+        for j in nums.indices.dropFirst(i + 1) {
+            if nums[i] + nums[j] == target {
+                return [i, j]
+            }
+        }
+    }
+    return [0]
+}
+
+func twoSumHashTable(nums: [Int], target: Int) -> [Int] {
+    // 辅助哈希表，空间复杂度 O(n)
+    var dic: [Int: Int] = [:]
+    // 单层循环，时间复杂度 O(n)
+    for i in nums.indices {
+        if let j = dic[target - nums[i]] {
+            return [j, i]
+        }
+        dic[nums[i]] = i
+    }
+    return [0]
+}
+
+@main
+enum LeetcodeTwoSum {
+    static func main() {
+        // ======= Test Case =======
+        let nums = [2, 7, 11, 15]
+        let target = 9
+        // ====== Driver Code ======
+        // 方法一
+        var res = twoSumBruteForce(nums: nums, target: target)
+        print("方法一 res = \(res)")
+        // 方法二
+        res = twoSumHashTable(nums: nums, target: target)
+        print("方法二 res = \(res)")
+    }
+}