c.cpp

// Problem C: Choose Your Words Carefully
// Author: Christopher Vo

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <map>
using namespace std;
typedef map<string, int> hist;

// compare histogram entries by their frequency
bool lessThan(const pair<string, int> & l, const pair<string, int> & r) {
  return l.second < r.second;
}

int main()
{
  hist hist;
  string line;

  // process input --------------------------------------------
  while (getline(cin, line)) {
    char c;
    int bw = 0, curr = 0, end = line.length();
    if (end == 0) continue;
    // skip to first alphanumeric in line
    while (curr <= end && !isalnum(line[curr])) curr++;
    bw = curr;
    // go through rest of line
    do {
      c = line[curr];
      // non-alphanumeric and EOL marks end of words
      if (!isalnum(c) || curr == end) {
        string word = line.substr(bw, curr - bw);
        for (int i = 0; i < word.length(); i++)
          word[i] = tolower(word[i]);
        // update histogram
        hist[word]++;
        // advance bw and curr to beginning of next word
        while (curr <= end && !isalnum(line[curr])) curr++;
        bw = curr;
      }
      curr++;
    } while (curr <= end);
  }

  // determine most-used word ---------------------------------
  int max = max_element(hist.begin(), hist.end(), lessThan)->second;
  cout << max << " occurrences" << endl;

  // print out all matching words, in any order. --------------
  hist::iterator it;
  for(it = hist.begin(); it != hist.end(); ++it)
    if(it->second >= max)
      cout << it->first << endl;
  return 0;
}

C.java

// Problem C: Choose Your Words Carefully
// Author: Christopher Vo

import java.util.*;

public class C {
  public static void main(String args[]) {
    HashMap<String, Integer> map = new HashMap<String, Integer>();
    Scanner sc = new Scanner(System.in).useDelimiter("[^a-zA-Z0-9]+");
    while (sc.hasNext()) {
      String word = sc.next().toLowerCase();
      Integer c = map.get(word);
      map.put(word, c != null ? c + 1 : 1);
    }
    int max = Collections.max(map.values());
    System.out.println(max + " occurrences");
    for(Map.Entry<String, Integer> e : map.entrySet()) {
      if(e.getValue().equals(max))
        System.out.println(e.getKey());
    }
  }
}