C语言，利用递归归并排序查找无序数组中第K大元素

以下是C语言利用递归归并排序查找无序数组中第K大元素的代码：

#include <stdio.h>

int merge(int arr[], int l, int m, int r) {
    int i, j, k;
    int n1 = m - l + 1;
    int n2 = r - m;
    int L[n1], R[n2];
    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1 + j];
    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2) {
        if (L[i] >= R[j]) {
            arr[k] = L[i];
            i++;
        }
        else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }
    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }
    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}

int mergeSort(int arr[], int l, int r, int k) {
    if (l < r) {
        int m = l + (r - l) / 2;
        mergeSort(arr, l, m, k);
        mergeSort(arr, m + 1, r, k);
        merge(arr, l, m, r);
    }
    if (r - l + 1 == k) {
        printf("%d", arr[r]);
        return arr[r];
    }
}

int main() {
    int arr[] = { 12, 3, 5, 7, 19 };
    int n = sizeof(arr) / sizeof(arr[0]);
    int k = 3;
    mergeSort(arr, 0, n - 1, k);
    return 0;
}

关于中文加密的问题，我可以提供以下代码作为参考：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void encrypt(char* str, int key) {
    int len = strlen(str);
    for (int i = 0; i < len; i++) {
        if (str[i] >= 'a' && str[i] <= 'z') {
            str[i] = (str[i] - 'a' + key) % 26 + 'a';
        }
        else if (str[i] >= 'A' && str[i] <= 'Z') {
            str[i] = (str[i] - 'A' + key) % 26 + 'A';
        }
        else if (str[i] >= '0' && str[i] <= '9') {
            str[i] = (str[i] - '0' + key) % 10 + '0';
        }
        else if (str[i] >= 0x4e00 && str[i] <= 0x9fa5) {
            str[i] = (str[i] - 0x4e00 + key) % (0x9fa5 - 0x4e00 + 1) + 0x4e00;
        }
    }
}

void decrypt(char* str, int key) {
    int len = strlen(str);
    for (int i = 0; i < len; i++) {
        if (str[i] >= 'a' && str[i] <= 'z') {
            str[i] = (str[i] - 'a' - key + 26) % 26 + 'a';
        }
        else if (str[i] >= 'A' && str[i] <= 'Z') {
            str[i] = (str[i] - 'A' - key + 26) % 26 + 'A';
        }
        else if (str[i] >= '0' && str[i] <= '9') {
            str[i] = (str[i] - '0' - key + 10) % 10 + '0';
        }
        else if (str[i] >= 0x4e00 && str[i] <= 0x9fa5) {
            str[i] = (str[i] - 0x4e00 - key + (0x9fa5 - 0x4e00 + 1)) % (0x9fa5 - 0x4e00 + 1) + 0x4e00;
        }
    }
}

int main() {
    char str[] = "Hello, World! 你好，世界！123456";
    int key = 3;
    printf("Original string: %s\n", str);
    encrypt(str, key);
    printf("Encrypted string: %s\n", str);
    decrypt(str, key);
    printf("Decrypted string: %s\n", str);
    return 0;
}