Q35 PepCoding | Count Of Subarrays With Equal Number Of 0s 1s And 2s

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Fri Jan 27 2023 11:13:20 GMT+0000 (Coordinated Universal Time)

Saved by @Ayush_dabas07

import java.util.*;

public class Main {

    public static int solution(int[] arr) {
        //make a hashmap<key,index> and traverse the array and keep adding key in the hashmap

//if the key repeats that means equal number of 0's,1's & 2's are present

//update frequency of the repeated key as we have to find the count of substrings 
        
        int ans = 0;
        HashMap<String,Integer> map = new HashMap<>();
        
        int count0 = 0 , count1 =0 , count2 =0 ;
        
        map.put("0#0" ,1 );
        for(int i =0 ;i  < arr.length ; i++){
            
            //update counts
            if(arr[i] == 0) count0++;
            else if(arr[i] == 1) count1++;
            else count2++;
            
            //find difference in counts
            int diff1 = count1-count0;
            int diff2 = count2-count1;
            
            //generate key
            String val = diff1 +"#"+diff2;
            
//if key is already present,this key will make subarrays with already present keys in the HM which is represented by frequency

            if(map.containsKey(val)){
                
                ans += map.get(val);
            }
            
            //add the subarrays in ans and update the frequency
                map.put(val , map.getOrDefault(val,0)+1);
            
        }
        
        return ans;
    }
    
    public static void main(String[] args) {
        Scanner scn = new Scanner(System.in);
        int n = scn.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = scn.nextInt();
        }
        System.out.println(solution(arr));
    }

}

https://www.pepcoding.com/resources/data-structures-and-algorithms-in-java-levelup/hashmap-and-heaps/count-of-subarrays-with-equal-number-of-0s-1s-and-2s-official/ojquestion

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