Q20 Find All Anagrams in a String - LeetCode

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Thu Jan 26 2023 06:36:19 GMT+0000 (Coordinated Universal Time)

Saved by @Ayush_dabas07

class Solution {
    public List<Integer> findAnagrams(String s, String p) {
        //baseCase
        if(p.length() > s.length())
        return new ArrayList<>();

        //make HM of p 
        HashMap<Character , Integer> small = new HashMap<>();   //for string  p
        for(int i =0 ; i< p.length();i++){
            char ch = p.charAt(i);
            small.put(ch , small.getOrDefault(ch,0)+1);
        }

        ArrayList<Integer> ans = new ArrayList<>();
        HashMap<Character,Integer> big = new HashMap<>();       //for string s

        //adding first p.length() chars in big

        for(int i =0 ; i< p.length();i++){
            char ch = s.charAt(i);
            big.put(ch , big.getOrDefault(ch,0)+1);
        }
        //now j will be at p.length()  and i  will be at 0 //or j - p.length()
        int j = p.length();
        
        while(j < s.length()){
            //first check if maps are equal
            if(big.equals(small))
            ans.add(j - p.length());

            //slide the window by adding and removing a character

            //add character
            char ch = s.charAt(j);
            big.put(ch , big.getOrDefault(ch,0)+1);

            //remove last character 
            ch = s.charAt(j - p.length());
            
            if(big.get(ch)==1)
            big.remove(ch);

            else
            big.put(ch , big.get(ch)-1);

            j++;
            
        }
        
        //checking the last window 
        if(big.equals(small))
        ans.add(j - p.length());


        return ans;
    }
}

https://leetcode.com/problems/find-all-anagrams-in-a-string/

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