Count Substrings with equal number of 0s, 1s and 2s in C++

We are given string str containing 0’s, 1’s, and 2’s only. The goal is to find all substrings of str that have equal numbers of 0’s 1’s and 2’s. If str is “12012”. Substrings with equal 0’s, 1’s, and 2’s will be “120”, “201” and “012”. The count will be 3.

Let us understand with examples.

Input − str=”112200120”

Output −Count of Substrings with an equal number of 0s, 1s, and 2s are − 5

Explanation − Substrings will be

str[0-5]=”112200”, str[1-6]=”122001”, str[5-7]=”012”, str[6-8]=”120”, str[7-0]=”201”

Input − str=”12012”

Output −Count of Substrings with an equal number of 0s, 1s, and 2s are: 3

Explanation − Substrings will be −

str[0-2]=”120” , str[1-3]=”201”, str[2-4]=”012”

The approach used in the below program is as follows

  • Take a string of integer values and calculate the length of a string

  • Pass the data to the function for further processing.

  • Take a temporary variable count to store the count of substrings with equal numbers of 0’s, 1’s, and 2’s.

  • Create a variable of type map which is mapping the pair to the frequencies of the given numbers.

  • Store 1 at pair (0,0) and start loop FOR from 0 till the length of a string.

  • Inside the loop, check IF str[i] = 0 then increment the count for 0’s, ELSE IF str[i] = 1 then increment the count for 1’s, ELSE increment the count for 2’s.

  • Set 0’s and 1’s to 0’s - 1’s and 0’s and 2’s to 0’s - 2’s.

  • Make a pair of zero_one and zero_two and set the count as count + map_pair of difference value which is calculated by making the pairs.

  • Increment the map_pair by 1.

  • Return count

  • Print the result.


 Live Demo

#include <bits/stdc++.h>
using namespace std;
int count_string(string str_1, int length_str1, string str_2, int length_str2){
   int count = INT_MAX;
   int arr_1[26] = { 0 };
   int arr_2[26] = { 0 };
   for (int i = 0; i < length_str1; i++){
      arr_1[str_1[i] - 'a']++;
   for (int i = 0; i < length_str2; i++){
      arr_2[str_2[i] - 'a']++;
   int alphabets = 26;
   for (int i = 0; i < alphabets; i++){
         count = min(count, arr_1[i] / arr_2[i]);
   return count;
int main(){
   string str_1 = "knowledge", str_2 = "know";
   int length_str1 = str_1.size();
   int length_str2 = str_2.size();
   cout<<"Count occurrences of a string that can be constructed from another given string are: "<<count_string(str_1,length_str1, str_2, length_str2);
   return 0;


If we run the above code it will generate the following output −

Count of Substrings with equal number of 0s, 1s and 2s are: 1

Updated on: 01-Dec-2020


Kickstart Your Career

Get certified by completing the course

Get Started