C语言常见算法
# C语言常见算法C语言中常用的算法可以分为以下几大类：
## 1. 排序算法
### 冒泡排序 (Bubble Sort)
```c
void bubbleSort(int arr[], int n) {
for (int i = 0; i < n-1; i++) {
for (int j = 0; j < n-i-1; j++) {
if (arr > arr) {
// 交换
int temp = arr;
arr = arr;
arr = temp;
}
}
}
}
```
### 选择排序 (Selection Sort)
```c
void selectionSort(int arr[], int n) {
for (int i = 0; i < n-1; i++) {
int min_idx = i;
for (int j = i+1; j < n; j++) {
if (arr < arr) {
min_idx = j;
}
}
// 交换
int temp = arr;
arr = arr;
arr = temp;
}
}
```
### 插入排序 (Insertion Sort)
```c
void insertionSort(int arr[], int n) {
for (int i = 1; i < n; i++) {
int key = arr;
int j = i - 1;
while (j >= 0 && arr > key) {
arr = arr;
j--;
}
arr = key;
}
}
```
### 快速排序 (Quick Sort)
```c
void quickSort(int arr[], int low, int high) {
if (low < high) {
int pi = partition(arr, low, high);
quickSort(arr, low, pi - 1);
quickSort(arr, pi + 1, high);
}
}
int partition(int arr[], int low, int high) {
int pivot = arr;
int i = (low - 1);
for (int j = low; j <= high - 1; j++) {
if (arr < pivot) {
i++;
swap(&arr, &arr);
}
}
swap(&arr, &arr);
return (i + 1);
}
void swap(int* a, int* b) {
int t = *a;
*a = *b;
*b = t;
}
```
## 2. 查找算法
### 线性查找 (Linear Search)
```c
int linearSearch(int arr[], int n, int x) {
for (int i = 0; i < n; i++) {
if (arr == x) {
return i;
}
}
return -1;
}
```
### 二分查找 (Binary Search)
```c
int binarySearch(int arr[], int l, int r, int x) {
while (l <= r) {
int m = l + (r - l) / 2;
if (arr == x) {
return m;
}
if (arr < x) {
l = m + 1;
} else {
r = m - 1;
}
}
return -1;
}
```
## 3. 递归算法
### 阶乘计算
```c
int factorial(int n) {
if (n == 0 || n == 1) {
return 1;
}
return n * factorial(n - 1);
}
```
### 斐波那契数列
```c
int fibonacci(int n) {
if (n <= 1) {
return n;
}
return fibonacci(n - 1) + fibonacci(n - 2);
}
```
## 4. 数学算法
### 最大公约数 (GCD)
```c
int gcd(int a, int b) {
if (b == 0) {
return a;
}
return gcd(b, a % b);
}
```
### 最小公倍数 (LCM)
```c
int lcm(int a, int b) {
return (a * b) / gcd(a, b);
}
```
### 素数判断
```c
int isPrime(int n) {
if (n <= 1) return 0;
for (int i = 2; i * i <= n; i++) {
if (n % i == 0) {
return 0;
}
}
return 1;
}
```
## 5. 字符串算法
### 字符串反转
```c
void reverseString(char* str) {
int n = strlen(str);
for (int i = 0; i < n / 2; i++) {
char temp = str;
str = str;
str = temp;
}
}
```
### 字符串比较
```c
int stringCompare(char *str1, char *str2) {
while (*str1 && *str2 && *str1 == *str2) {
str1++;
str2++;
}
return *str1 - *str2;
}
```
## 6. 数据结构相关算法
### 链表反转
```c
struct Node* reverseList(struct Node* head) {
struct Node* prev = NULL;
struct Node* current = head;
struct Node* next = NULL;
while (current != NULL) {
next = current->next;
current->next = prev;
prev = current;
current = next;
}
return prev;
}
```
### 二叉树遍历 (前序)
```c
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
};
void preorderTraversal(struct TreeNode* root) {
if (root == NULL) return;
printf("%d ", root->val);
preorderTraversal(root->left);
preorderTraversal(root->right);
}
```
## 7. 其他常用算法
### 位操作算法
```c
// 计算二进制中1的个数
int countSetBits(int n) {
int count = 0;
while (n) {
count += n & 1;
n >>= 1;
}
return count;
}
// 判断是否是2的幂
int isPowerOfTwo(int n) {
return n && (!(n & (n - 1)));
}
```
### 动态规划 - 斐波那契数列 (优化版)
```c
int fib(int n) {
int a = 0, b = 1, c, i;
if (n == 0) return a;
for (i = 2; i <= n; i++) {
c = a + b;
a = b;
b = c;
}
return b;
}
```
这些算法是C语言编程中常见的基础算法，掌握它们对于提高编程能力和解决实际问题非常有帮助。
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