/* File: majority.c

   A simple recursive function to determine
   whether a character appears in a majority of
   a string.
*/

#include <stdio.h>
#include <string.h>

int count(char c, char *str, int low, int high) {
   
   if (high < low) return 0 ;
   
   if (str[high] == c) {
      return 1 + count(c, str, low, high-1) ;
   } else {
      return count(c, str, low, high-1) ;
   }
}


/* Return the character that appears as more than
   half the characters.  Return 0 if no such character.
*/
char majority(char *str, int low, int high) {
   int mid, count1 = 0, count2 = 0 ;
   float half ;
   char c1, c2 ;
   
   if (high < low) return 0 ;
   if (low == high) return str[low] ;

   /* midpoint of string */
   mid = (high + low) / 2 ;

   /* half the length,use floating point value */
   half = (high - low + 1.0) / 2.0 ;

   c1 = majority(str, low, mid) ;
   c2 = majority(str, mid+1, high) ;

   if (c1 != 0) count1 = count(c1, str, low, high) ;
   if (c2 != 0) count2 = count(c2, str, low, high) ;

   if (count1 > half) {
      return c1 ;
   } else if (count2 > half) {
      return c2 ;
   } else {
      return 0 ;
   }
    
}


main(int argc, char *argv[]){
  char c, *str ;
  int n ;

  if (argc != 2) {
     printf("Usage: majority str\n") ;
     exit(1) ;
  }

  str = argv[1] ;
  n = strlen(str) - 1 ;

  c = majority(str, 0, n) ; 

  if (c != 0) {
     printf("%c is the majority character\n", c) ;
  } else {
     printf("No majority character\n") ;
  }
}