题目：给你一个数字n0。将它的每一个位的数字按递增排序生成数a，按递减排序生成数b，

            新的数字为n1 = a-b，下次依照相同方法计算n1，知道出现循环，问计算了多少次。

分析：数论、模拟。直接模拟计算就可以，利用hash表判重。

说明：注意初始化。

#include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           using namespace std;//hashtypedef struct hash_node{ int path; hash_node* next;}hnode;hnode* tabel[1002];hnode nodeh[1002];int hash_size;void hash_initial(){ memset(tabel, 0, sizeof(tabel)); hash_size = 0;}int hash_find(int s){ int v = s%1001; for (hnode* p = tabel[v] ; p ; p = p->next) if (p->path == s) return 1; nodeh[hash_size].next = tabel[v]; nodeh[hash_size].path = s; tabel[v] = &nodeh[hash_size ++]; return 0;}//hash endint buf[11];int number(int *a, int n){ int value = 0; for (int i = 0 ; i < n ; ++ i) { value *= 10; value += a[i]; } return value;}int cmp1(int a, int b) { return a < b; }int cmp2(int a, int b) { return a > b; }int main(){ int n,count,sum,a,b; while (~scanf("%d",&n) && n) { printf("Original number was %d\n",n); hash_initial(); sum = 0; do { hash_find(n); sum ++; count = 0; while (n) { buf[count ++] = n%10; n /= 10; } sort(buf, buf+count, cmp2); a = number(buf, count); sort(buf, buf+count, cmp1); b = number(buf, count); printf("%d - %d = %d\n",a,b,n = a-b); }while (!hash_find(n)); printf("Chain length %d\n\n",sum); } return 0;}