面试编程题（字符串）

1 字符串转整数

long long StrToIntCore(const char* str, bool minus);

enum Status {kValid = 0, kInvalid};
int g_nStatus = kValid;

int StrToInt(const char* str)
{
    g_nStatus = kInvalid;
    long long num = 0;

    if(str != NULL && *str != '') 
    {
        bool minus = false;
        if(*str == '+')
            str ++;
        else if(*str == '-') 
        {
            str ++;
            minus = true;
        }

        if(*str != '') 
        {
            num = StrToIntCore(str, minus);
        }
    }

    return (int)num;
}

long long StrToIntCore(const char* digit, bool minus)
{
    long long num = 0;

    while(*digit != '') 
    {
        if(*digit >= '0' && *digit <= '9') 
        {
            int flag = minus ? -1 : 1;
            num = num * 10 + flag * (*digit - '0');

            if((!minus && num > 0x7FFFFFFF) 
                || (minus && num < (signed int)0x80000000))
            {
                num = 0;
                break;
            }

            digit++;
        }
        else 
        {
            num = 0;
            break;
        }
    }

    if(*digit == '') 
    {
        g_nStatus = kValid;
    }

    return num;
}

2字符串基本操作函数原型

int strlen(const char * str)
{
    assert(str!=NULL);
    int len = 0;
    while((*str++) !=‘0’)
        len++;
    return len;
}

int strcmp(const char* str1,const char* str2)
{
    assert(str!=NULL && str2!=NULL);
    int ret = 0;
    while(!(ret = *(unsigned char*)str1-*(unsigned char*)str2)&& *str)
    {
        str1++;
        str2++;
    }
    if(ret<0)    ret = -1;
    else if(ret > 0)     ret = 1;
    return     ret;
}
char * strcat(char *strDest,const char *strSrc)
{
    char * address = strDest;
    assert((strDest!=NULL) && (strSrc != NULL));
    while(*strDest)
    {
        strDest++;
    }
    while(*strDest++ = *strSrc++);
    return address;
}
char *  strcpy(char* strDest,const char * strSrc)
{
    assert(strDest!= NULL && strSrc !=NULL);
    char * strD = strDest;
    while((*strDest++=*strSrc++)!='');
    return strD;
}

3字符串匹配 KMP

int kmp_search(const char* src,int slen,const char* patn,int plen,const int * nextval,int pos)
{
    int i =pos , j=0;
    while(i<slen && j<plen)
    {
        if(j==-1 || src[i]==patn[j]){++i;++j;}
        else
        {
            j = nextval[j];
        }
    }
    if(j>=plen) return i-plen;
    else return -1;
}

void get_nextval(char const* ptrn,int plen,int *nextval)
{
    int i = 0;
    nextval[i] = -1;
    int j=-1;
    while(i<plen-1)
    {
        if(j==-1||ptrn[i]==ptrn[j]){++i;++j;nextval[i]=j;}
        else
            j=nextval[j];
     }
}

//改进
void get_nextval(char const* ptrn,int plen,int *nextval)
{
    int i = 0;
    nextval[i] = -1;
    int j=-1;
    while(i<plen-1)
    {
        if(j==-1||ptrn[i]==ptrn[j])
        {
            ++i;
            ++j;
               if(ptrn[i]!=ptrn[j])
                    nextval[i]=j;
                else
                    nextval[i]=nextval[j];
        }
        else
            j = nextval[j];
     }
}

//最基础的BF算法
char* strFind(const char*str,const char* substr)
{
    assert(str!=NULL && substr!=NULL );
    int m = strlen(str);
    int n = strlen(substr);
    if(m < n)
        return NULL;
    for(int i=0; i<=m-n;i++)
    {
        for(int j=0;j<n;j++)
        {
            if(str[i+j]!=substr[j])
                break;
        }
        if(j==n)
            return str+i;
    }
    return NULL;
}

4 最长回文子串Manacher

/*最长回文子串长度
Manacher算法
*/
void Manacher(char* str)
{
    int len = strlen(str);
    int i,id,maxid = 0;
    int newstr_len =0;
    newstr[newstr_len++] = '@';    
    for (i = 0; i < len; i++){  
        newstr[newstr_len++] = '#';
        newstr[newstr_len++] = str[i];
    }  
    newstr[newstr_len++] = '#';
    newstr[newstr_len++] = '$';

    int * p = new int[newstr_len];
    for(i=1;i<newstr_len-1;i++)
    {
        if(maxid > i)
            p[i] = min(p[2*id-i],maxid-i);
        else
            p[i] = 0;
        while(newstr[i+1+p[i]]==newstr[i-1-p[i]])
            p[i]++;
        if(p[i]+i>maxid)
        {
            maxid = p[i]+i;
            id = i;
        }
    }
    int maxlen = 0;
    int centerIndex = 0;
     for (i = 1; i<newstr_len-1;i++){  
         if(p[i] > maxlen)
         {
             maxlen = p[i];
             centerIndex = i;
         }
     }  
     delete[] p;
    printf("%d:",maxlen);
     for(int i=(centerIndex-1-maxlen)/2;i<=maxlen;i++)
         putchar(str[i]);
     putchar('
');
}