C语言面试算法题（一）

1.求组合数： 求n个数（1....n）中k个数的组合....
           如：combination(5,3)
  要求输出：543，542，541，532，531，521，432，431，421，321，

/*  求组合数： 求n个数（1....n）中k个数的组合....            如：combination(5,3)   要求输出：543，542，541，532，531，521，432，431，421，321， */ #include <stdio.h> #include <error.h> int pop(int *); int push(int ); void combination(int ,int); int stack[3]={0}; int top = -1; int main() {   int n,m;     n = 5;     m = 3;   combination(n,m);   printf("\n"); } void combination(int m,int n) {   int temp = m;   push(temp);   while(1)   {     if(1==temp)     {       if(pop(&temp) && stack[0]==n)         break;     }     else if(push(--temp))     {       printf("%d%d%d\n",stack[0],stack[1],stack[2]);       pop(&temp);     }   } } int push(int i) {   stack[++top]=i;   if(top<2)     return 0;   else     return 1; } int pop(int *i) {   *i = stack[top--];   if(top>=0)     return 0;   else     return 1; }

2.、用指针的方法，将字符串“ABCD1234efgh”前后对调显示

#include <stdio.h> #include <string.h> int main() {   char str[]="ABCD123efgh";   int length = strlen(str);   char *p1= str;   char *p2 = str+length -1;   while(p1<p2)   {     char c = *p1;     *p1 = *p2;     *p2 = c;     ++p1;     --p2;   }   printf("str now is %s\n",str);   return 1; }

3.给定字符串A和B,输出A和B中的最大公共子串。比如A="aocdfe" B="pmcdfa" 则输出"cdf"

#include <stdio.h> #include <stdlib.h> #include <string.h> char *commanstring(char shortstring[],char longstring[]) {   int i,j;   char *substring = malloc(256);   if(strstr(longstring,shortstring)!=NULL)     return shortstring;   for(i=strlen(shortstring)-1;i>0;i--)   {     for(j=0;j<=strlen(shortstring)-i;j++)     {       memcpy(substring,&shortstring[j],i);     substring[i]='\0';     if(strstr(longstring,substring)!=NULL)       return substring;     }   }   return NULL; } void main(void) {   char *str1 = "aocdfe";   char *str2 = "pmcdfa";   char *comman = NULL;   if(strlen(str1)>strlen(str2))     comman= commanstring(str2,str1);   else     comman = commanstring(str1,str2);   printf("the longest comman string is:%s\n",comman);     }