Write a function: alternate(s1,s2) The function gets two strings s1, s2 as input and prints a new string. The output string will alternate between the two input strings, repeatedly taking a single character from each. For example: alternate(‘abcd’, ‘1234’) → ‘a1b2c3d4’ alternate(‘HHH’, ‘aaa’) → ‘HaHaHa’ alternate(‘bnn’, ‘aaaaaa’) → ‘bananaaaa’ alternate(‘BNNaa’, ‘AAA’) → ‘BANANAaa’ If the input strings are not in the same length, alternate between the strings and then add the remaining characters of the longer string (see last two examples).

Here's the Python code for the `alternate` function:

def alternate(s1, s2):
    result = ""
    # use the length of the shorter string
    length = min(len(s1), len(s2))
    for i in range(length):
        result += s1[i] + s2[i]
    # add the remaining characters of the longer string
    if len(s1) > length:
        result += s1[length:]
    elif len(s2) > length:
        result += s2[length:]
    print(result)

You can call this function with two input strings, like this:

alternate('abcd', '1234')
alternate('HHH', 'aaa')
alternate('bnn', 'aaaaaa')
alternate('BNNaa', 'AAA')

The output will be:

a1b2c3d4
HaHaHa
bananaaaa
BANANAaa

相关问题

Collecting package metadata (current_repodata.json): ...working... done Solving environment: ...working... failed with initial frozen solve. Retrying with flexible solve. Collecting package metadata (repodata.json): ...working... done Solving environment: ...working... failed with initial frozen solve. Retrying with flexible solve. PackagesNotFoundError: The following packages are not available from current channels: - crefi Current channels: - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main/linux-64 - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main/noarch - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/msys2/linux-64 - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/msys2/noarch - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/r/linux-64 - https://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/r/noarch - https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/pytorch/linux-64 - https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/pytorch/noarch - https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/msys2/linux-64 - https://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/msys2/noarch To search for alternate channels that may provide the conda package you're looking for, navigate to https://anaconda.org and use the search bar at the top of the page.

这个错误提示表明在当前的镜像源中找不到名为 "crefi" 的包。请按照以下步骤进行排查：

1. 检查包的名称是否正确，确保没有拼写错误。
2. 检查网络连接是否正常，可以尝试使用其他网络或者更换镜像源。
3. 在终端中运行以下命令更新 conda：

conda update conda

然后再尝试安装包。

4. 如果仍然无法找到包，可以尝试在 https://anaconda.org 上搜索该包，看看是否有其他可用的镜像源提供该包。

希望这些解决方案能帮助到您！如果还有其他问题，请随时提问。

The Sleeping Teaching Assistant A university computer science department has a teaching assistant (TA) who helps undergraduate students with their programming assignments during regular office hours. The TA’s office is rather small and has room for only one desk with a chair and computer. There are three chairs in the hallway outside the office where students can sit and wait if the TA is currently helping another student. When there are no students who need help during office hours, the TA sits at the desk and takes a nap. If a student arrives during office hours and finds the TA sleeping, the student must awaken the TA to ask for help. If a student arrives and finds the TA currently helping another student, the student sits on one of the chairs in the hallway and waits. If no chairs are available, the student will come back at a later time. Using POSIX threads, mutex locks, and/or semaphores, implement a solution that coordinates the activities of the TA and the students. Details for this assignment are provided below. Using Pthreads, begin by creating N students. Each will run as a separate thread. The TA will run as a separate thread as well. Student threads will alternate between programming for a period of time and seeking help from the TA. If the TA is available, they will obtain help. Otherwise, they will either sit in a chair in the hallway or, if no chairs are available, will resume programming and will seek help at a later time. If a student arrives and notices that the TA is sleeping, the student must notify the TA using a semaphore. When the TA finishes helping a student, the TA must check to see if there are students waiting for help in the hallway. If so, the TA must help each of these students in turn. If no students are present, the TA may return to napping. Perhaps the best option for simulating students programming—as well as the TA providing help to a student—is to have the appropriate threads sleep for a random period of time using the sleep() API:

This is a programming assignment that requires the use of POSIX threads, mutex locks, and/or semaphores to coordinate the activities of the TA and the students. Here is one possible solution:

1. Create a mutex lock and two semaphores: one for the TA and one for the students waiting in the hallway.
2. Create N student threads and one TA thread.
3. Each student thread should loop indefinitely, alternating between programming and seeking help from the TA.
4. When a student needs help, they should try to acquire the mutex lock. If the TA is sleeping, the student should signal the TA semaphore and wait on the student semaphore. If the TA is helping another student, the student should wait on the student semaphore.
5. When the TA wakes up, they should try to acquire the mutex lock. If there are students waiting in the hallway, the TA should signal the student semaphore N times to wake up the students. The TA should then help each student in turn, releasing the mutex lock after each one is helped.
6. If there are no students waiting, the TA should release the mutex lock and go back to sleep.

Here is some sample code to implement this solution:

#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define N 10 // number of students
#define CHAIRS 3 // number of chairs in hallway

pthread_t students[N], ta;
pthread_mutex_t mutex;
sem_t student_sem, ta_sem;

int waiting = 0;

void *student(void *arg) {
    int id = *(int*)arg;
    while (1) {
        // program for a random amount of time
        sleep(rand() % 10 + 1);
        printf("Student %d needs help\n", id);
        pthread_mutex_lock(&mutex);
        if (waiting < CHAIRS) {
            // there is a free chair in the hallway
            waiting++;
            printf("Student %d waiting in hallway (%d/%d)\n", id, waiting, CHAIRS);
            pthread_mutex_unlock(&mutex);
            sem_wait(&student_sem);
            waiting--;
        } else {
            // no free chairs in the hallway
            printf("Student %d will come back later\n", id);
            pthread_mutex_unlock(&mutex);
        }
        // get help from TA
        printf("Student %d getting help from TA\n", id);
        // help for a random amount of time
        sleep(rand() % 5 + 1);
    }
}

void *ta_helper(void *arg) {
    while (1) {
        // sleep until a student wakes us up
        sem_wait(&ta_sem);
        while (1) {
            pthread_mutex_lock(&mutex);
            if (waiting == 0) {
                // no students waiting, go back to sleep
                pthread_mutex_unlock(&mutex);
                break;
            }
            // help the next student in line
            waiting--;
            sem_post(&student_sem);
            printf("TA helping a student (%d/%d)\n", waiting, CHAIRS);
            pthread_mutex_unlock(&mutex);
            // help for a random amount of time
            sleep(rand() % 5 + 1);
        }
    }
}

int main() {
    // initialize mutex lock and semaphores
    pthread_mutex_init(&mutex, NULL);
    sem_init(&student_sem, 0, 0);
    sem_init(&ta_sem, 0, 0);
    // create student threads
    int student_ids[N];
    for (int i = 0; i < N; i++) {
        student_ids[i] = i;
        pthread_create(&students[i], NULL, student, &student_ids[i]);
    }
    // create TA thread
    pthread_create(&ta, NULL, ta_helper, NULL);
    // wait for threads to finish
    for (int i = 0; i < N; i++) {
        pthread_join(students[i], NULL);
    }
    pthread_join(ta, NULL);
    // clean up mutex lock and semaphores
    pthread_mutex_destroy(&mutex);
    sem_destroy(&student_sem);
    sem_destroy(&ta_sem);
    return 0;
}

Note that this is just one possible solution and there may be other ways to implement the same behavior using different synchronization primitives.