task1:
源代码:
#include<iostream> #include<string> #include<vector> #include<algorithm> template<typename T> void output(const T &c);void test1(); void test2(); void test3();int main(){std::cout<<"测试1: \n";test1();std::cout<<"\n测试2: \n";test2();std::cout<<"\n测试3: \n";test3(); }template <typename T> void output(const T &c){for(auto &i : c)std::cout<<i<<' ';std::cout<<'\n';}void test1(){using namespace std;string s0{"0123456789"};cout <<"s0= "<<s0<<endl;string s1(s0);reverse(s1.begin(),s1.end());cout <<"s1= "<<s1<<endl;string s2(s0.size(),' ');reverse_copy(s0.begin(),s0.end(),s2.begin());cout<<"s2= "<<s2<<endl; }void test2(){using namespace std;vector<int> v0{2,0,4,9};cout<<"v0: "; output(v0);vector<int> v1{v0};reverse(v1.begin(),v1.end());cout<<"v1: ";output(v1);vector<int> v2{v0};reverse_copy(v0.begin(),v0.end(),v2.begin());cout<<"v2: "; output(v2); }void test3(){using namespace std;vector<int> v0{0,1,2,3,4,5,6,7,8,9};cout<<"v0: ";output(v0);vector<int> v1{v0};rotate(v1.begin(),v1.begin()+1,v1.end());cout<<"v1: ";output(v1);vector<int> v2{v0};rotate(v2.begin(),v2.begin()+2,v2.end());cout<<"v2: ";output(v2);vector<int> v3{v0};rotate(v3.begin(),v3.end()-1,v3.end());cout<<"v3: "; output(v3);vector<int> v4{v0};rotate(v4.begin(),v4.end()-2,v4.end());cout<<"v4: ";output(v4) ;}
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问题回答:
问题1:reverse是直接修改输入序列，将元素反转；reverse_copy是将输入序列反转后的结果复制到另一个序列中，不会改变原始序列。
问题2:rotate通过将序列中某个位置的元素一道开头，同时保持其他元素的相对位置来改变元素元素顺序。三个参数(first,middle,last),rotate会将middle至last位置的元素移动至起始位置，并将first至middle位置的元素整体移动至末尾。
task2:
源代码:
#include <iostream> #include <vector> #include <algorithm> #include <numeric> #include <iomanip> #include <cstdlib> #include <ctime>template<typename T> void output(const T &c);int generate_random_number(); void test1(); void test2();int main() {std::srand(std::time(0));std::cout << "测试1: \n";test1();std::cout << "\n测试2: \n";test2(); }template <typename T> void output(const T &c) {for(auto &i: c)std::cout << i << ' ';std::cout << '\n'; }int generate_random_number() {return std::rand() % 101; }void test1() {using namespace std;vector<int> v0(10);generate(v0.begin(), v0.end(), generate_random_number);cout << "v0: "; output(v0);vector<int> v1{v0};sort(v1.begin(), v1.end());cout << "v1: "; output(v1);vector<int> v2{v0};sort(v2.begin()+1, v2.end()-1);cout << "v2: "; output(v2); }void test2() {using namespace std;vector<int> v0(10);generate(v0.begin(), v0.end(), generate_random_number);cout << "v0: "; output(v0);auto min_iter = min_element(v0.begin(), v0.end());auto max_iter = max_element(v0.begin(), v0.end());cout << "最小值: " << *min_iter << endl;cout << "最大值: " << *max_iter << endl;auto ans = minmax_element(v0.begin(), v0.end());cout << "最小值: " << *(ans.first) << endl;cout << "最大值: " << *(ans.second) << endl;double avg1 = accumulate(v0.begin(), v0.end(), 0.0) / v0.size();cout << "均值: " << fixed << setprecision(2) << avg1 << endl;sort(v0.begin(), v0.end());double avg2 = accumulate(v0.begin()+1, v0.end()-1, 0.0) / (v0.size()-2);cout << "去掉最大值、最小值之后，均值: " << avg2 << endl; }
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问题回答:
问题1:generate算法的作用是用函数动态生成的值填充序列。
问题2:只需要一次遍历序列，时间复杂度更低，效率更高。
问题3:效果是等同的。lambda的表达式用法:在需要函数的地方直接定义，减少代码跳转，更简洁也便于捕获外部变量。
task3
源代码:
#include<iostream> #include<string> #include<algorithm> #include<cctype>unsigned char func(unsigned char c); void test1(); void test2();int main() {std::cout << "测试1：字符串大小写转换\n";test1();std::cout << "\n测试2：字符变换\n";test2(); }unsigned char func(unsigned char c) {if(c=='z')return 'a';if(c=='Z')return 'A';if(std::isalpha(c))return static_cast<unsigned char>(c+1);return c; }void test1() {std::string s1{"Hello World 2049!"};std::cout << "s1 = " << s1 << '\n';std::string s2;for(auto c:s1)s2+=std::tolower(c);std::cout << "s2 = " << s2 << '\n';std::string s3;for(auto c:s1)s3+=std::toupper(c);std::cout << "s3 = " << s3 << '\n'; }void test2() {std::string s1{"I love cosmos!"};std::cout << "s1 = " <<s1 << '\n';std::string s2(s1.size(),' ');std::transform(s1.begin(),s1.end(),s2.begin(),func);std::cout << "s2 = " << s2 << '\n'; }
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问题回答:
问题1:func的功能是把字母字符转换为下一个字符。
问题2:tolower的功能是将大写字母转换为对应的小写字母。toupper的功能是将小写字母转换为对应的大写字母。
问题3:第一个参数s1.begin()是指元素的起始位置；第二个参数s1.end()是指元素的结束位置；第三个参数s2.begin()是指变换后结果的存储起始位置；第四个参数func是指执行transform所依赖的算法逻辑。
如果把s2.begin()改成s1.begin()，
变化后的结果会覆盖s1的内容，s2却仍为初始化时的空格。
task4
源代码:
#include <iostream> #include <string> #include <algorithm> bool is_palindrome(const std::string &s); bool is_palindrome_ignore_case(const std::string &s); int main() { using namespace std; string s; // 多组输入，直到按下Ctrl+Z结束测试 while(cin >> s) { cout << boolalpha << "区分大小写: " << is_palindrome(s) << "\n" << "不区分大小写: " << is_palindrome_ignore_case(s) << "\n\n"; } } // 函数is_palindrome定义 // 待补足 // ××× bool is_palindrome(const std::string &s) {int i=0,j=s.size()-1;while(i<j){if(i<j){if(s[i]!=s[j])return false;}i++;j--;}return true; }//indrome_ignore_case定义 bool is_palindrome_ignore_case(const std::string &s) {using namespace std;string s2;for(char c:s)s2+=tolower(c);int i=0,j=s2.size()-1;while(i<j){if(i<j){if(s2[i]!=s2[j])return false;}i++;j--;}return true; }
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观察与思考:
答：需要将cin>>s改为getline(cin,s)，因为getline会读取包括空格在内的一整行输入。
task5
源代码:
#include <iostream> #include <string> #include <algorithm> std::string dec2n(int x, int n = 2); int main() { int x; while(std::cin >> x) { std::cout << "十进制: " << x << '\n' << "二进制: " << dec2n(x) << '\n' << "八进制: " << dec2n(x, 8) << '\n' << "十二进制: " << dec2n(x, 12) << '\n' << "十六进制: " << dec2n(x, 16) << '\n' << "三十二进制: " << dec2n(x, 32) << "\n\n"; } } // 函数dec2n定义 std::string dec2n(int x, int n) {if (x==0) {return "0"; }std::string result;while (x> 0) {int r=x%n;char d;if (r<10) {d='0'+r; }else {d='A'+r-10;} result.push_back(d);x=x/n; }std::reverse(result.begin(), result.end());return result; }
运行截图:
task6
源代码:
#include<iostream> #include<vector> #include<algorithm> #include<iomanip> int main() {using namespace std;char c;int i=0; cout << ' ' << ' ';for(c='a';c<='z';c++)cout << ' ' << c ;cout << endl;for(i=2;i<=27;i++){cout << setw(2) << right << i-1 << ' ';for(c='A'+(i-1);c<'A'+(i-1)+26;c++){cout << (char)(c>'Z'?c-26:c) << ' ';} cout << endl;}return 0;}
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task7
源代码:
include <iostream> #include <cstdlib> #include <ctime> #include <iomanip> int main() {srand(time(0)); int correctCount = 0; const int t=10; for (int i=0;i<t;++i) {int a=rand()%10+1; int b;int operation=rand()%4; char opChar;int correctAnswer;switch (operation) {case 0: //加法b=rand()%10+1;opChar='+';correctAnswer =a+b;break;case 1: //减法b=rand()%a+1; opChar='-';correctAnswer=a-b;break;case 2: //乘法b=rand()%10+1;opChar='*';correctAnswer=a*b;break;case 3: //除法b=rand()%10+1;while(a%b!=0) { a=rand()%10+1;b=rand()%10+1;}opChar = '/';correctAnswer=a/b;break;}std::cout <<a<<" "<<opChar<<" "<<b<<"=";int userAnswer;std::cin>>userAnswer;if (userAnswer==correctAnswer){correctCount++;}}double accuracy=static_cast<double>(correctCount)/t*100;std::cout << std::fixed << std::setprecision(2) << "正确率: " << accuracy << "%" << std::endl;return 0; }
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