/* ------------------------------------------------------ *//* PROGRAM Lexical Order of k-Subsets :                   *//*    Given a n-element set {1,2,3,...,n} and a k <= n,   *//* this program lists all k-element subsets of {1,2,..,n} *//* in lexical order.                                      *//*                                                        *//* Copyright Ching-Kuang Shene               July/08/1989 *//* ------------------------------------------------------ */ #include  <stdio.h>#include  <stdlib.h> #define   MAXSIZE    20#define   LOOP        1 void main(void){     int  set[MAXSIZE];     int  n;     int  k;     int  position;     int  i, j;     char line[100];      printf("\nAll k Elements Subsets from a n Elements Set");     printf("\n============================================");     printf("\n\nNumber of Elements in the Set --> ");     gets(line);     n = atoi(line);     printf("\n\nNumber of Elements in Subset ---> ");     gets(line);     k = atoi(line);      for (i = 0; i < k; i++)  /* initialize the subset to */          set[i] = i + 1;     /* {1,2,3,...,k}            */     printf("\n{%d", set[0]); /* display it               */     for (j = 1; j < k; j++)          printf(",%d", set[j]);     printf("}");      position = k - 1;        /* 'position' indicates the */     while (LOOP) {           /* pos to be increased      */          if (set[k-1] == n)  /* if last pos is full, then*/               position--;    /* move position left       */          else                /* or if not full, then the */               position = k - 1; /* pos is always the last*/          set[position]++;    /* so add one to the pos.   */          for (i = position+1; i < k; i++) /* add inc. all*/               set[i] = set[i-1] + 1; /* pos to its right */           printf("\n{%d", set[0]); /* display it.         */          for (j = 1; j < k; j++)               printf(",%d", set[j]);          printf("}");           if (set[0] >= n-k+1) break; /* if 1st pos full  */     }}

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