cs106x-lecture8(Autumn 2017)-SPL实现

打卡cs106x(Autumn 2017)-lecture8

(以下皆使用SPL实现，非STL库，后续课程结束会使用STL实现)

1、reverseLines

Write a recursive function named reverseLines that accepts as its parameter a reference to a file input stream (ifstream) and prints the lines of that file in reverse order. For example, if an input file named poem.txt contains the following text:

Roses are red,
Violets are blue.
All my base
Are belong to you.

Then the call of reverseLines("poem.txt"); should produce the following console output:

Are belong to you.
All my base
Violets are blue.
Roses are red,

You may assume that the input file exists and is readable.

Constraints: Your solution should read the file only once, not make multiple passes over the file data. Your function must be recursive.

解答：

#include 
#include 
#include 
#include "console.h"

using namespace std;


void reverseLines(ifstream& input);

int main() {
    ifstream input;
    input.open("poem.txt");
    if (input.is_open()) {
        reverseLines(input);
    }
    input.close();
    return 0;
}

void reverseLines(ifstream& input) {
    string line;
    if (getline(input, line)) { // recursive case
        reverseLines(input);
        cout << line << endl;
    }
    // base case: no line
    // do nothing
}

2、printBinary

Write a recursive function named printBinary that accepts an integer and prints that number's representation in binary (base 2) to the console. For example, the call of printBinary(43); should print 101011 . You do not need to print an endl character at the end of your output.

If the integer is negative, print the binary representation preceded by a minus sign. For example, the call of printBinary(-6); should print -110 .

Constraints: Do not use any loops. Do not solve this problem by converting the number into a string. Do not solve it by using the pow function or any form of computing exponents; that is inefficient and not needed to solve the problem. Do not declare any auxiliary collections such as a vector or map. Do not solve it by using the ostream manipulation functionality such as setbase.

解答：

#include 
#include 
#include "console.h"

using namespace std;

void printBinary(int n);

int main() {
    printBinary(43);
    return 0;
}

void printBinary(int n) {
    if (n < 0) {
        cout << "-";
        printBinary(-n);
    } else if (n <= 1) {
        cout << n;
    } else {
        int last = n % 2;
        int remind = n / 2;
        printBinary(remind);
        printBinary(last);
    }
}

3、crawl

Write a recursive function named crawl that accepts a string for a file or directory name as a parameter and prints information about that file or directory. If the name represents a normal file, just print its name. If the name represents a directory, print its name and information about every file/directory inside it, indented by 4 spaces at each level. For example, the call of crawl("course") might print the following information about your course directory:

course
    handouts
        lecture-schedule.xls
        syllabus.doc
    homework
        1-gameoflife
            GameOfLife.zip
            life.cpp
            life.h

Constraints: Your function must be recursive, though you may use a loop to help you as appropriate.

解答：

#include 
#include 
#include "console.h"
#include "filelib.h"
#include "vector.h"

using namespace std;

void crawl(const string& filename, const string& indentation="");

int main() {
    crawl("../BlankProject");
    return 0;
}

void crawl(const string& filename, const string& indentation) {
    if (isDirectory(filename)) {
        Vector v = listDirectory(filename);
        for (string vs: v){
            cout << indentation << vs << endl;
            string indentations = indentation + "    ";
            crawl(filename + '/' + vs, indentations);
        }
    }
}