Program to parse the Molecules and get the Atoms count

Given a chemical formula as a string, the task is to get the count of atoms in this chemical formula.
Examples:

Input: str = "Fe2H3OH"
Output: Fe 2
        H 4
        O 1

Input: str = "NaCl2NaO2"
Output: Na 2
        Cl 2
        O 2

Approach: The below approach work in Java programming language: 

• Take LinkedHashMap to store atom name(Key) and count(value) in insertion order.
• Check if the string character is lowercase then add to the previous uppercase string character.
• Check if the string contains the number then add to the count(value) to their particular atom name(key).
• Print the atom name(key) as well as count(value). 

Below is the implementation of the above approach :

C++

#include <bits/stdc++.h>
using namespace std;

void getCount(string str)
{
  // Use LinkedHashmap to store
  // elements in insertion order
  map<string, int> mp;

  for (int i = 0; i < str.length(); i++) {
    int count = 0;

    // Convert the string element into character
    char c = str.at(i);
    string a = " ";

    // Convert the character element
    // into string element
    a = string(1, c);

    // Check string contains the Capital A - Z value.
    if (a.find_first_of("ABCDEFGHIJKLMNOPQRSTUVWXYZ") != string::npos) {

      for (int j = i + 1; j < str.length(); j++) {

        char d = str.at(j);
        string b = string(1, d);

        // Check string contains the small a-z value.
        if (b.find_first_of("abcdefghijklmnopqrstuvwxyz") != string::npos) {

          a += b;

          if (mp.find(a) == mp.end())
            mp[a] = 1;
          else
            mp[a] += 1;
          count = 1;
        }

        // Check string contains the number value.
        else if (b.find_first_of("0123456789") != string::npos) {

          int k = stoi(b);
          mp[a] = k;
          count = 1;
        }

        else {
          i = j - 1;
          break;
        }
      }

      if (count == 0) {
        if (mp.find(a) == mp.end())
          mp[a] = 1;
        else
          mp[a] += 1;
      }
    }
  }

  cout << "\nAtom count:" << endl;
  for (auto entry : mp)
    cout << entry.first << " " << entry.second << endl;

  mp.clear();
}

// Driver code
int main()
{
  string str = "Fe2H3OH";
  cout << "Given molecule: " << str << endl;
  getCount(str);
  return 0;
}

// This code is contributed by surajrasr7277.

Java

// Java program to parse the molecule
// and get the atoms count

import java.io.*;
import java.util.*;

class GFG {

    static void getCount(String str)
    {

        // Use LinkedHashmap to store
        // elements in insertion order
        Map<String, Integer> mp
            = new LinkedHashMap<String, Integer>();

        for (int i = 0; i < str.length(); i++) {
            int count = 0;

            // Convert the string element into character
            char c = str.charAt(i);
            String a = " ";

            // Convert the character element
            // into string element
            a = String.valueOf(c);

            // Check string contains the Capital A - Z value.
            if (a.matches("[A-Z]")) {

                for (int j = i + 1; j < str.length(); j++) {

                    char d = str.charAt(j);
                    String b = String.valueOf(d);

                    // Check string contains the small a-z value.
                    if (b.matches("[a-z]")) {

                        a += b;

                        if (mp.get(a) == null)
                            mp.put(a, 1);
                        else
                            mp.put(a, mp.get(a) + 1);
                        count = 1;
                    }

                    // Check string contains the number value.
                    else if (b.matches("[\\d]")) {

                        int k = Integer.parseInt(b);
                        mp.put(a, k);
                        count = 1;
                    }

                    else {
                        i = j - 1;
                        break;
                    }
                }

                if (count == 0) {
                    if (mp.get(a) == null)
                        mp.put(a, 1);
                    else
                        mp.put(a, mp.get(a) + 1);
                }
            }
        }

        System.out.println("\nAtom count:");
        for (Map.Entry<String, Integer>
                 entry : mp.entrySet())
            System.out.println(entry.getKey()
                               + " "
                               + entry.getValue());

        mp.clear();
    }

    // Driver code
    public static void main(String[] args)
    {
        String str = "Fe2H3OH";
        System.out.println("Given molecule: "
                           + str);
        getCount(str);
    }
}

Python3

# Python program to parse the molecule
# and get the atoms count
def get_count(s):
    # Use dictionary to store elements in insertion order
    mp = {}

    i = 0
    while i < len(s):
        count = 0

        # Convert the string element into character
        c = s[i]

        # Check string contains the Capital A - Z value.
        if c.isupper():
            a = " "

            # Convert the character element
            # into string element
            a += c

            j = i + 1
            while j < len(s):
                d = s[j]

                # Check string contains the small a-z value.
                if d.islower():
                    a += d

                    if a not in mp:
                        mp[a] = 1
                    else:
                        mp[a] += 1
                    count = 1

                # Check string contains the number value.
                elif d.isdigit():
                    k = int(d)
                    mp[a] = k
                    count = 1
                else:
                    i = j - 1
                    break
                j += 1

            if count == 0:
                if a not in mp:
                    mp[a] = 1
                else:
                    mp[a] += 1

        i += 1

    print("\nAtom count:")
    for key, value in mp.items():
        print(key, value)

    mp.clear()

# Driver code
str = "Fe2H3OH"
print("Given molecule:", str)
get_count(str)

C#

using System;
using System.Collections.Generic;

namespace GFG
{
  class Program
  {

    // Method to get the count of atoms
    static void getCount(String str)
    {
      // Use LinkedHashmap to store
      // elements in insertion order
      Dictionary<String, int> mp
        = new Dictionary<String, int>();

      for (int i = 0; i < str.Length; i++)
      {
        int count = 0;

        // Convert the string element into character
        char c = str[i];
        String a = " ";

        // Convert the character element
        // into string element
        a = c.ToString();

        // Check string contains the Capital A - Z value.
        if (System.Text.RegularExpressions.Regex.IsMatch(a, "[A-Z]"))
        {

          for (int j = i + 1; j < str.Length; j++)
          {

            char d = str[j];
            String b = " ";

            // Convert the character element
            // into string element
            b = d.ToString();

            // Check string contains the small a-z value.
            if (System.Text.RegularExpressions.Regex.IsMatch(b, "[a-z]"))
            {

              a += b;

              if (!mp.ContainsKey(a))
                mp.Add(a, 1);
              else
                mp[a] += 1;
              count = 1;
            }

            // Check string contains the number value.
            else if (System.Text.RegularExpressions.Regex.IsMatch(b, "[\\d]"))
            {
              int k = Convert.ToInt32(b);
              mp[a] = k;
              count = 1;
            }

            else
            {
              i = j - 1;
              break;
            }
          }

          if (count == 0)
          {
            if (!mp.ContainsKey(a))
              mp.Add(a, 1);
            else
              mp[a] += 1;
          }
        }
      }

      Console.WriteLine("\nAtom count:");
      foreach (KeyValuePair<String, int> entry in mp)
        Console.WriteLine(entry.Key
                          + " "
                          + entry.Value);

      mp.Clear();
    }

    // Driver code
    public static void Main(String[] args)
    {
      String str = "Fe2H3OH";
      Console.WriteLine("Given molecule: "
                        + str);
      getCount(str);
    }
  }
}
// This code added By Ajax

Javascript

// Javascript program to parse the molecule
// and get the atoms count
function get_count(s) {
// Use Map to store elements in insertion order
let mp = new Map();

let i = 0;
while (i < s.length) {
let count = 0;
// Convert the string element into character
let c = s.charAt(i);

// Check string contains the Capital A - Z value.
if (c.match(/[A-Z]/)) {
  let a = " ";

  // Convert the character element
  // into string element
  a += c;

  let j = i + 1;
  while (j < s.length) {
    let d = s.charAt(j);

    // Check string contains the small a-z value.
    if (d.match(/[a-z]/)) {
      a += d;

      if (!mp.has(a)) {
        mp.set(a, 1);
      } else {
        mp.set(a, mp.get(a) + 1);
      }
      count = 1;
    }

    // Check string contains the number value.
    else if (d.match(/[0-9]/)) {
      let k = parseInt(d);
      mp.set(a, k);
      count = 1;
    } else {
      i = j - 1;
      break;
    }
    j += 1;
  }

  if (count == 0) {
    if (!mp.has(a)) {
      mp.set(a, 1);
    } else {
      mp.set(a, mp.get(a) + 1);
    }
  }
}
i += 1;
}

console.log("\nAtom count:");
for (let [key, value] of mp) {
console.log(key, value);
}

mp.clear();
}

// Driver code
let str = "Fe2H3OH";
console.log("Given molecule:", str);
get_count(str);

Output:

Given molecule: Fe2H3OH

Atom count:
Fe 2
H 4
O 1

Time Complexity: O(N), Here N is the length of the string.
Auxiliary Space: O(N), The extra space is used in HashMap.