数据结构之字符串

#include <iostream>
#include <cstring>
#include <stack>
#include <cstring>
using namespace std;

//字符串复制
void cpystr(char*s1,char *s2)
{
    int n2=strlen(s2);
    int j=0;
    for(int i=0; i<n2; i++)
    {
        s1[j++]=s2[i];
    }
    s1[j]='';
}

//字符串拼接
char* concat(char *s1,char *s2)
{
    int n1=strlen(s1),n2=strlen(s2);
    char *s=new char[n1+n2+1];
    int j=0;
    for(int i=0; i<n1; i++)
    {
        s[j++]=s1[i];
    }
    for(int i=0; i<n2; i++)
    {
        s[j++]=s2[i];
    }
    s[j]='';
    return s;
}


//求子串
char* subString(char *s,int pos,int len)
{
    char *t=new char[len];
    int j=0;
    for(int i=pos; i<pos+len; i++)
    {
        t[j++]=s[i];
    }
    t[j]='';
    return t;
}

//?????
int compare(char *s1,char *s2)
{
    if(s1==NULL&&s2!=NULL)
    {
        return -1;
    }
    if(s2==NULL&&s1!=NULL)
    {
        return 1;
    }
    if(s1==NULL&&s2==NULL)
    {
        return 0;
    }
    while(*s1&&*s2&&*s1==*s2)
    {
        s1++;
        s2++;
    }
    if(*s1==*s2)
    {
        return 0;
    }
    return *s1-(*s2);
}


//求子串的定位问题Brute-Force
int Index_BF(char* s1,char* s2)
{
    int i,j;
    int len1=strlen(s1);
    int len2=strlen(s2);
    for(i=0;i<len1-len2+1;i++)
    {
        j=0;
        for(;j<len2;j++)
        {
            if(s1[i+j]!=s2[j])
                break;
        }
        if(j==len2)
            return i;
    }
    return -1;
}


//全排列
void permutation(char* a,int begin,int end)
{
    int i,j;
    if(begin == end)    //一到递归的出口就输出数组，此数组为全排列
    {
        for(i=0; i<=end; i++)
            cout<<a[i];
        cout<<endl;
    }
    else
    {
        for(j=begin; j<=end; j++)
        {
            swap(a[j],a[begin]);//for循环将begin~end中的每个数放到begin位置中去
            permutation(a,begin+1,end);//假设begin位置确定，那么对begin+1~end中的数继续递归
            swap(a[j],a[begin]);//假设begin位置确定，那么对begin+1~end中的数继续递归
        }
    }
}
int main()
{
    char *s1=new char[20];
    char *s2=new char[20];
    cin>>s1>>s2;

    char *s=concat(s1,s2);
    cout<<"concat():"<<s<<endl;

    char *sub=subString(s,2,4);
    cout<<"subString(s,2,4):"<<sub<<endl;

    cout<<"s1:"<<s1<<endl;
    cout<<"s2:"<<s2<<endl;
    cout<<"compare():"<<compare(s1,s2)<<endl;

    cpystr(s1,s2);
    cout<<"strcpy():"<<s1<<endl;

    cout<<"s2:"<<s2<<endl;
    //permutation(s2,0,strlen(s2)-1);
    cout<<endl;

    cout<<"index('456123','23'):"<<Index_BF("4561230","23")<<endl;


    delete []s1;
    delete []s2;
    delete []s;
    delete [] sub;
    return 0;
}