zoj 1405 Tanning Salon

#include<stdio.h>#include<string.h>int sert(char x,int y,char a[]){    int k=1;    for(;y>=0;y--)      if(a[y]==x)      {        k=0;        break;      }   return k;}   int main(){   int i,k,n,len,leave,curr;   char a[53];   scanf("%d",&n);   while(n!=0)   {      getchar();  leave=curr=0;      scanf("%s",a);      len=strlen(a);       for(i=0;i<len;i++)      {         if(sert(a[i],i-1,a))         {curr++;if(curr>n)  leave++;         }          else curr--;      }      if(leave!=0)        printf("%d customer(s) walked away.n",leave);      else        printf("All customers tanned successfully.n");      scanf("%d",&n);   }   return 0;}