1.

#include <iostream>
#include <cstring>
#include <algorithm>
#include<string>
#include<stack>
using namespace std;
void trans(string &s1,char a,char b)
{
    for(int i=0;i<s1.size();i++)
    {
        if(s1[i]==a)
        {
            s1[i]=b;
        }
    }
}
int main() {
    string s1;
    char a,b;
    cin>>s1>>a>>b;
    trans(s1,a,b);
    cout<<s1<<endl;
}

2.

#include <iostream>
#include <cstring>
#include <algorithm>
#include<string>
#include<stack>
using namespace std;
void trans(string &s1)
{
   for(int i=0,j=s1.size()-1;i<j;i++,j--)
   {
       swap(s1[i],s1[j]);
   }
}
int main() {
    string s1;
    cin>>s1;
    trans(s1);
    cout<<s1<<endl;
}

3

#include <iostream>
#include <string>
using namespace std;

void delete_string(string &s, char c) {
    int n = s.size();
    int i = 0;

    while (i < n) {
        if (s[i] == c) {
            // 将当前字符及其后面的字符前移
            for (int j = i; j < n - 1; j++) {
                s[j] = s[j + 1];
            }
            n--;   
        } else {
            i++;   
        }
    }
    s.resize(n);
}

int main() {
    string s;
    char c;
    cin >> s >> c;
    cout<<s.size()<<endl;
    delete_string(s, c);
    cout << s << endl;
    cout<<s.size()<<endl;
    return 0;
}
#include <iostream>
#include <string>
using namespace std;

void delete_string(string &s, char c) {
    int n = s.size();
    int i = 0;
    int index=0;
    while (i < n) {
        if(s[i]!=c)
        {
            s[index++]=s[i];
        }
        i++;
        }
    s.resize(index);
}

int main() {
    string s;
    char c;
    cin >> s >> c;
    delete_string(s, c);
    cout << s << endl;
    return 0;
}

4

#include <iostream>
#include <string>
using namespace std;

void delete_string(string &s, int a,int b) {

 int n=s.size();
 int index=0;
 if(a+b>n)b=n-a;
 for(int i=0;i<n;i++)
 {
     if(i<a||i>=a+b)
     {
         s[index++]=s[i];
     }
 }
 s.resize(index);
}

int main() {
    string s;
    int a,b;
    getline(cin,s);
    cin>>a>>b;
    delete_string(s,a,b);
    cout<<s<<endl;
}

3

#include <iostream>
#include <string>
using namespace std;

void replace_substring(string &s1, const string &s2, int i, int j) {
    // 确保 i 和 j 在有效范围内
    if (i < 0 || i >= s1.size() || j < i || j >= s1.size()) {
        cout << "Invalid indices" << endl;
        return;
    }

    // 生成替换后的字符串
    s1 = s1.substr(0, i) + s2 + s1.substr(j + 1);
}

int main() {
    string s1, s2;
    int i, j;

    // 读取输入
    cin >> s1 >> s2 >> i >> j;

    // 调用函数进行替换
    replace_substring(s1, s2, i, j);

    // 输出结果
    cout << s1 << endl;

    return 0;
}

4

#include <iostream>
#include <string>
using namespace std;

int count_times(string s,string s1)
{
    int i=0;//主串指针
    int j=0;//模式串指针
    int count=0;//记录匹配次数
    int n=s.size();
    int n1=s1.size();
    while(i<n&&j<n1)
    {
        if(s[i]==s1[j])
        {
            i++;
            j++;
        }
        else
        {
            j=0;
            i++;
        }
        if(j==n1-1)
        {
            count++;
            j=0;
        }
    }
    return count;
}

int main() {
    string s, s1;
    cin>>s>>s1;
    cout<<count_times(s,s1)<<endl;
}

5

#include <iostream>
#include <cstring>
using namespace std;
struct Node {
    char val;
    Node *next;

    Node(int x) : val(x), next(NULL) {}
};
Node *CreateListWithTail(char s[], int n) {
    Node*dummy=new Node(-1);
    Node*tail=dummy;
    for(int i=0;i<n;i++)
    {
        Node*node=new Node(s[i]);
        tail->next=node;
        tail=node;
    }
    return dummy->next;
}
void print(Node *head)
{
    for (Node *p = head; p; p = p->next)
        cout << p->val << ' ';
    cout << endl;
}
char first_unfind(Node*list1,Node*list2)
{
    while (list1) {
        Node* cur2 = list2;
        bool is_find = false;
        while (cur2) {
            if (cur2->val == list1->val) {
                is_find = true;
                break;
            }
            cur2 = cur2->next;
        }
        if (!is_find) {
            return list1->val;
        }
        list1 = list1->next;
    }
    return '\0';  // 如果所有字符都在list2中找到，返回 '\0'

}
int main() {
    char s1[]="abcde";
    char s2[]="abccc";
    int n1 =strlen(s1);
    int n2 =strlen(s2);
    Node *list1 =CreateListWithTail(s1, n1);
    Node *list2= CreateListWithTail(s2, n2);
    cout<<first_unfind(list1,list2)<<endl;
    return 0;
}