Hash Maps and Dictionaries

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

#define MAX 50

// A tiny by-hand map: parallel arrays of words and their counts.
char keys[MAX][20];
int counts[MAX];
int size = 0;

// Find the slot for a word, or -1 if it is not stored yet.
int find(const char *word) {
    for (int i = 0; i < size; i++) {
        if (strcmp(keys[i], word) == 0) return i;
    }
    return -1;
}

// Put: add 1 to a word's count, creating it if new.
void add(const char *word) {
    int idx = find(word);
    if (idx == -1) {
        strcpy(keys[size], word);
        counts[size] = 1;
        size++;
    } else {
        counts[idx]++;
    }
}

// Remove: delete a word by shifting the last item into its slot.
void removeKey(const char *word) {
    int idx = find(word);
    if (idx == -1) return;
    strcpy(keys[idx], keys[size - 1]);
    counts[idx] = counts[size - 1];
    size--;
}

int main(void) {
    const char *words[] = {"apple", "banana", "apple", "cherry", "banana", "apple"};
    int n = 6;

    for (int i = 0; i < n; i++) add(words[i]);   // count every word

    int a = find("apple");                       // Get
    printf("apple count: %d\n", counts[a]);

    printf("has cherry? %s\n", find("cherry") != -1 ? "yes" : "no"); // Contains

    removeKey("banana");                         // Remove

    printf("Remaining:\n");                      // Iterate
    for (int i = 0; i < size; i++) {
        printf("%s -> %d\n", keys[i], counts[i]);
    }
    return 0;
}

apple count: 3
has cherry? yes
Remaining:
apple -> 3
cherry -> 1

#include <iostream>
#include <unordered_map>
#include <string>
#include <vector>
using namespace std;

int main() {
    vector<string> words = {"apple", "banana", "apple", "cherry", "banana", "apple"};

    unordered_map<string, int> freq;        // make an empty map

    for (const string &word : words) {
        freq[word]++;                       // Put: add 1 to this word's count
    }

    cout << "apple count: " << freq["apple"] << "\n";              // Get

    cout << "has cherry? "                                         // Contains
         << (freq.count("cherry") ? "yes" : "no") << "\n";

    freq.erase("banana");                                          // Remove

    cout << "Remaining:\n";                                        // Iterate
    for (const auto &pair : freq) {
        cout << pair.first << " -> " << pair.second << "\n";
    }
    return 0;
}

apple count: 3
has cherry? yes
Remaining:
cherry -> 1
apple -> 3

import java.util.HashMap;
import java.util.Map;

public class WordCount {
    public static void main(String[] args) {
        String[] words = {"apple", "banana", "apple", "cherry", "banana", "apple"};

        Map<String, Integer> freq = new HashMap<>();   // make an empty map

        for (String word : words) {
            freq.put(word, freq.getOrDefault(word, 0) + 1);  // Put: count this word
        }

        System.out.println("apple count: " + freq.get("apple"));   // Get

        System.out.println("has cherry? " +                        // Contains
            (freq.containsKey("cherry") ? "yes" : "no"));

        freq.remove("banana");                                     // Remove

        System.out.println("Remaining:");                          // Iterate
        for (Map.Entry<String, Integer> e : freq.entrySet()) {
            System.out.println(e.getKey() + " -> " + e.getValue());
        }
    }
}

apple count: 3
has cherry? yes
Remaining:
apple -> 3
cherry -> 1

def main():
    words = ["apple", "banana", "apple", "cherry", "banana", "apple"]

    freq = {}                              # make an empty dict

    for word in words:
        freq[word] = freq.get(word, 0) + 1  # Put: count this word

    print("apple count:", freq["apple"])    # Get

    print("has cherry?", "yes" if "cherry" in freq else "no")  # Contains

    del freq["banana"]                      # Remove

    print("Remaining:")                     # Iterate
    for word, count in freq.items():
        print(word, "->", count)

main()

apple count: 3
has cherry? yes
Remaining:
apple -> 3
cherry -> 1

function main() {
  const words = ["apple", "banana", "apple", "cherry", "banana", "apple"];

  const freq = new Map();                 // make an empty Map

  for (const word of words) {
    freq.set(word, (freq.get(word) || 0) + 1);  // Put: count this word
  }

  console.log("apple count:", freq.get("apple"));   // Get

  console.log("has cherry?", freq.has("cherry") ? "yes" : "no"); // Contains

  freq.delete("banana");                            // Remove

  console.log("Remaining:");                        // Iterate
  for (const [word, count] of freq) {
    console.log(word, "->", count);
  }
}

main();

apple count: 3
has cherry? yes
Remaining:
apple -> 3
cherry -> 1