几道简单的面试题

1、寻找一个单向链表的倒数第n个节点；

2、二分查找以及二分查找寻找上下界；

3、求交叉链表的第一个交叉节点；

#include <assert.h>#include <stdio.h>#include <stdlib.h>using namespace std ;struct _link_node{    int data ;    struct _link_node *next ;} ;struct _link_node* create_linklist(int data[],int len){    assert(data!=NULL) ;    struct _link_node *pRoot = (struct _link_node*)malloc(sizeof(struct _link_node)) ;    //pRoot->next = NULL ;    struct _link_node *pTmp = pRoot ;    for(int i=0;i<len;i++){        pTmp->next=(struct _link_node*)malloc(sizeof(struct _link_node)) ;        pTmp->next->data = data[i] ;        pTmp = pTmp->next ;    }    pTmp->next = NULL ;    return pRoot ;}struct _link_node* print_link(struct _link_node* pRoot){    struct _link_node *pTmp = pRoot ;    while(pTmp->next!=NULL){        printf("%d,",pTmp->next->data) ;        pTmp=pTmp->next ;    }}struct _link_node* get_reverse_n(struct _link_node* pRoot,int n){    assert(pRoot!=NULL) ;    struct _link_node *pPre = pRoot ;    struct _link_node *pTail = pRoot ;    int cnt = 0 ;    /*使用两个指针，第一个指针比第一个指针先走n步，两个指针再一起移动，    当先走指针走向末尾时，另外一个指针所指向的位置就是倒数第n个*/    while(cnt<n){        if(pPre==NULL){            return NULL ;        }        cnt++ ;        pPre=pPre->next ;    }    while(pPre!=NULL&&pPre->next!=NULL){        pPre=pPre->next ;        pTail=pTail->next ;    }    return pTail->next ;}void PrintMeet(){    int hour=0 ;    int minutes=0 ;    for(int i=1;i<6;i++){//模拟时针每走一小时，角度是30度        hour+=30 ;        for(int j=0;j<60;j++){//模拟秒针走，一步角度为6；            minutes+=6 ;            if(minutes%360==hour){                printf("time=%d:%d\n",hour/30,minutes%360/6) ;            }        }    }}int binary_search(int array[],int low,int high,int target){    if(low>high||array[high]<target){//advance abort        return -1 ;    }    int mid = low+((high-low)>>1) ;    while(low<=high){        mid = low+((high-low)>>1) ;        if(array[mid]<target){            low = mid+1 ;        }else if(array[mid]>target){            high = mid-1 ;        }else{            return mid ;        }    }    return -1 ;}int binary_search1(int array[],int low,int high,int target){    if(low>high){        return -1 ;    }else{        int mid = low+((high-low)>>1) ;        if(array[mid]>target){            high = mid-1 ;            binary_search1(array,low,high,target) ;        }else if(array[mid]<target){            low = mid + 1 ;            binary_search1(array,low,high,target) ;        }else{            return mid ;        }    }}int binary_find_upper_bound(int array[],int low,int high,int target){    if(low>high||array[high]<target){//advance abort        return -1 ;    }    int mid =low + ((high-low)>>1) ;    while(low<high){        if(array[mid]>target){            high = mid ;        }else{            low = mid+1 ;        }        mid = low+((high-low)>>1) ;    }    return array[mid] ;}int binary_find_lower_bound(int array[],int low,int high,int target){    if(low>high||array[high]<target){//advance abort        return -1 ;    }    int mid = low+((high-low)>>1) ;    while(low<high){        if(array[mid]<target){            low = mid ;        }else{            high=mid-1 ;        }        mid = low + ((high-low+1)>>1) ;//note:here we must add 1 to compute mid    }    return array[mid] ;}int find_first_cross_node(struct _link_node*pFirst, struct _link_node *pSecond){    assert(pFirst!=NULL&&pSecond!=NULL) ;    int len_first=0 ;    int len_second=0 ;    struct _link_node *pTmp1=pFirst ;    struct _link_node *pTmp2=pSecond ;//first compute length of the two link list    while(pTmp1->next!=NULL){        pTmp1=pTmp1->next ;        len_first++ ;    }    while(pTmp2->next!=NULL){        pTmp2=pTmp2->next ;        len_second++ ;    }// if not have cross ,return -1    if(pTmp1!=pTmp2){//if not cross        return -1 ;    }//compare length of the two link list and difference of two link list length,//and decide which list should move first    int b_first_long=len_first>len_second ;    int diff=b_first_long?(len_first-len_second):(len_second-len_first) ;//the longer list should move diff steps    if(b_first_long){        pTmp1= pFirst ;        while(diff--){            pTmp1=pTmp1->next ;            printf("%d+",diff) ;        }        pTmp2 = pSecond ;    }else{        pTmp2=pSecond ;        while(diff--){            pTmp2=pTmp2->next ;        }        pTmp1 = pFirst ;    }//compute the last positon and the position = diff + last move    int location=b_first_long?(len_first-len_second):(len_second-len_first) ;    while(pTmp1!=pTmp2) {        pTmp1=pTmp1->next ;        pTmp2=pTmp2->next ;        location++ ;    }    return location ;}void create_cross_linklist(struct _link_node* pFirst, struct _link_node *pSecond,int len1,int len2,int position){    assert(pFirst!=NULL&&pSecond!=NULL) ;    struct _link_node *pTmp1 = pFirst ;    struct _link_node *pTmp2 = pSecond ;    int cnt = 0;    if(len1>len2){        assert((len2+position)<len1) ;        while(cnt<len2){            pTmp1 = pTmp1->next ;            pTmp2 = pTmp2->next ;            cnt++ ;        }        cnt=0;        while(cnt<position){            pTmp1=pTmp1->next ;            cnt++ ;        }        pTmp2->next = pTmp1 ;    }else{        assert((len1+position)<len2) ;        while(cnt<len1){            pTmp1 = pTmp1->next ;            pTmp2 = pTmp2->next ;            cnt++ ;        }        cnt=0 ;        while(cnt<position){            pTmp2 = pTmp2->next ;            cnt++ ;        }        pTmp1->next = pTmp2 ;    }}int main(){    int array[]={1,2,3,4,5,6,7,8,9,10,11,12,13,24} ;    int array1[]={2,3,4,6,1,3} ;    int len = sizeof(array)/sizeof(array[0]) ;    int len1 = sizeof(array1)/sizeof(array1[0]) ;    struct _link_node *pRoot1 = create_linklist(array,len) ;    struct _link_node *pRoot2 = create_linklist(array1,len1) ;    create_cross_linklist(pRoot1,pRoot2,len,len1,2) ;    printf("find first cross_node begin............\n") ;    printf("len=%d,len1=%d\n",len,len1) ;    int location = find_first_cross_node(pRoot1,pRoot2) ;    printf("first cross node at %d position\n",location) ;    printf("find first cross_node end............\n\n") ;    printf("binary search bound begin..........\n") ;    printf("location=%d\n",binary_search1(array,0,len-1,24)) ;    printf("upperbound=%d\n",binary_find_upper_bound(array,0,len-1,9)) ;    printf("lowerbound=%d\n",binary_find_lower_bound(array,0,len-1,9)) ;    printf("binary search bound end..........\n\n") ;    printf("find reciprocal n node begin..........\n") ;    struct _link_node *pRoot=create_linklist(array,len) ;    struct _link_node *pTmp=get_reverse_n(pRoot,3) ;    printf("data=%d\n",pTmp->data) ;    printf("find reciprocal n node end..........\n") ;}