面试中经常出现的算法

二分查找的代码.int bfind(int* a,int len,int val){    int m = len/2;    int l = 0;    int r = len;    while(l!=m && r!= m)    {        if(a[m] > val)        {            r = m;            m = (m+l)/2;        }        else if(a[m] < val)        {            l = m;            m = (m+r)/2;        }        else            return m;    }    return -1;   //没有找到}写出在母串中查找子串出现次数的代码.int count1(char* str,char* s){    char* s1;    char* s2;    int count = 0;    while(*str!='\0')    {        s1 = str;        s2 = s;        while(*s2 == *s1&&(*s2!='\0')&&(*s1!='0'))        {            s2++;            s1++;        }        if(*s2 == '\0')            count++;        str++;    }    return count;}查找第一个匹配子串位置,如果返回的是s1长度len1表示没有找到size_t find(char* s1,char* s2)    {        size_t i=0;         size_t len1 = strlen(s1)        size_t len2 = strlen(s2);        if(len1-len2<0) return len1;        for(;i        {            size_t m = i;            for(size_t j=0;j            {                if(s1[m]!=s2[j])                    break;                m++;            }            if(j==len)                break;        }        return i    }写出快速排序或者某种排序算法代码快速排序:int partition(int* a,int l,int r){    int i=l-1,j=r,v=a[r];    while(1)    {        while(a[++i]        while(a[--j]>v) if(j<=i) break;        if(i>=j)            break;        swap(a[i],a[j]);    }    swap(a[i],a[r]);    return i;}void qsort(int* a,int l,int r){    if(l>=r) return;    int i = partition(a,l,r);    qsort(a,l,i-1);    qsort(a,i+1,r);}冒泡排序:void buble(int *a,int n){    for(int i=0;i    {        for(int j=1;j        {            if(a[j]            {                int temp=a[j];                a[j] = a[j-1];                a[j-1] = temp;            }        }    }}插入排序：void insertsort(int* a,int n){    int key;    for(int j=1;j    {        key = a[j];        for(int i=j-1;i>=0&&a[i]>key;i--)        {            a[i+1] = a[i];        }        a[i+1] = key;    }}出现次数相当频繁实现strcmp函数int strcmp11(char* l,char* r){    assert(l!=0&&r!=0);    while(*l == *r &&*l != '\0') l++,r++;    if(*l > *r)        return 1;    else if(*l == *r)        return 0;    return -1;}实现字符串翻转void reserve(char* str){    assert(str != NULL);    char * p1 = str;    char * p2 = str-1;    while(*++p2);         //一般要求不能使用strlen    p2 -= 1;    while(p1    {        char c = *p1;        *p1++ = *p2;        *p2-- = c;   }}将一个单链表逆序struct list_node{    list_node(int a,list_node* b):data(a),next(b) //这个为了测试方便    {}    int data;    list_node* next;};void reserve(list_node* phead){        list_node* p = phead->next;        if(p == NULL || p->next == NULL) return; //只有头节点或一个节点        list_node* p1=p->next;        p->next=NULL;        while(p1!=NULL)        {            p = p1->next;            p1->next = phead->next;            phead->next = p1;            p1 = p;        }}测试程序：    list lt;    lt.phead = new list_node(0,0);    lt.phead->next = new list_node(1,0);    lt.phead->next->next = new list_node(2,0);    lt.phead->next->next->next = new list_node(3,0);    lt.reserve();    list_node * p = lt.phead;    while(p)    {        coutnext;    }循环链表的节点对换和删除。//双向循环list_node* earse(list_node* node){    // if(node == rear) return node->next;    //对于头节点可判断也可不判断。最好加上    list_node* next = node->next;    next->prev = node->prev;    node->prev->next = next;    delete node;    retrun next;}//单项循环list_node* earse(list_node* node){    // if(node == rear) return node->next;    //对于头节点可判断也可不判断。最好加上    list_node* p = rear;     while(p->next != node) p=p->next;   p->next = node->next;    delete node;    retrun p->next;}将一个数字字符串转换为数字."1234" -->1234int atoii(char* s){    assert(s!=NULL);    int num = 0;    int temp;    while(*s>'0' && *s<'9')    {        num *= 10;        num += *s-'0';        s++;    }    return num;}出现次数相当频繁.实现任意长度的整数相加或者相乘功能。void bigadd(char* num,char* str,int len){    for(int i=len;i>0;i--)    {        num[i] += str[i];        int j = i;        while(num[j]>=10)        {            num[j--] -= 10;            num[j] += 1;        }    }}.写函数完成内存的拷贝void* memcpy( void *dst, const void *src, unsigned int len ){    register char *d;    register char *s;    if (len == 0)        return dst;    if ( dst > src )   //考虑覆盖情况    {        d = (char *)dst + len - 1;        s = (char *)src + len - 1;        while ( len >= 4 )   //循环展开，提高执行效率        {            *d-- = *s--;            *d-- = *s--;            *d-- = *s--;            *d-- = *s--;            len -= 4;        }        while ( len-- )         {            *d-- = *s--;        }    }     else if ( dst < src )     {        d = (char *)dst;        s = (char *)src;        while ( len >= 4 )        {            *d++ = *s++;            *d++ = *s++;            *d++ = *s++;            *d++ = *s++;            len -= 4;        }        while ( len-- )        {            *d++ = *s++;        }    }    return dst;}出现次数相当频繁编写类String的构造函数、析构函数和赋值函数，已知类String的原型为：class String{      public:      String(const char *str = NULL); // 普通构造函数    String(const String &other); // 拷贝构造函数   ~ String(void); // 析构函数 String & operate =(const String &other); // 赋值函数      private:     char *m_data; // 用于保存字符串      };解答：//普通构造函数String::String(const char *str){       if(str==NULL)       {               m_data = new char[1]; // 得分点：对空字符串自动申请存放结束标志'\0'的空                                  　//加分点：对m_data加NULL 判断              *m_data = '\0';       }           else       {        int length = strlen(str);        m_data = new char[length+1]; // 若能加 NULL 判断则更好        strcpy(m_data, str);       }}// String的析构函数String::~String(void){       delete [] m_data; // 或delete m_data;}//拷贝构造函数String::String(const String &other) 　　　// 得分点：输入参数为const型{            int length = strlen(other.m_data);       m_data = new char[length+1]; 　　　　//加分点：对m_data加NULL 判断       strcpy(m_data, other.m_data);    }//赋值函数String & String::operate =(const String &other) // 得分点：输入参数为const型{            if(this == &other)                 　　//得分点：检查自赋值               return *this;          delete [] m_data;           　　　　//得分点：释放原有的内存资源       int length = strlen( other.m_data );             m_data = new char[length+1]; 　//加分点：对m_data加NULL 判断       strcpy( m_data, other.m_data );          return *this;    　　　　　　　　//得分点：返回本对象的引用}剖析：能够准确无误地编写出String类的构造函数、拷贝构造函数、赋值函数和析构函数的面试者至少已经具备了C++基本功的60%以上！在这个类中包括了指针类成员变量m_data，当类中包括指针类成员变量时，一定要重载其拷贝构造函数、赋值函数和析构函数，这既是对C++程序员的基本要求，也是《Effective　C++》中特别强调的条款。实现strcpychar * strcpy( char *strDest, const char *strSrc ) {　assert( (strDest != NULL) && (strSrc != NULL) );char *address = strDest; 　while( (*strDest++ = * strSrc++) != ‘\0’ );return address;}编写一个函数，作用是把一个char组成的字符串循环右移n个。比如原来是“abcdefghi”如果n=2，移位后应该是“hiabcdefgh” 函数头是这样的：//pStr是指向以'\0'结尾的字符串的指针//steps是要求移动的nvoid LoopMove ( char * pStr, int steps ){//请填充...}解答：正确解答1：void LoopMove ( char *pStr, int steps ){    int n = strlen( pStr ) - steps;    char tmp[MAX_LEN];        strcpy ( tmp, pStr + n );     strcpy ( tmp + steps, pStr);        *( tmp + strlen ( pStr ) ) = '\0';    strcpy( pStr, tmp );}正确解答2：void LoopMove ( char *pStr, int steps ){    int n = strlen( pStr ) - steps;    char tmp[MAX_LEN];        memcpy( tmp, pStr + n, steps );       memcpy(pStr + steps, pStr, n );         memcpy(pStr, tmp, steps );    }