Problem_7_PermutationInAString.java

package Sliding_Window;

// Problem Statement: Permutation in a String (hard)
// LeetCode Question: 567. Permutation in String

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

public class Problem_7_PermutationInAString {
    public boolean findPermutation(String str,  String pattern){
        int windowStart = 0, matched = 0;
        Map<Character, Integer> charFrequencyMap = new HashMap<>();
        for (char chr : pattern.toCharArray()) {
            charFrequencyMap.put(chr, charFrequencyMap.getOrDefault(chr, 0) + 1);
        }
        for (int windowEnd = 0; windowEnd < str.length(); windowEnd++) {
            char rightChar = str.charAt(windowEnd);
            if (charFrequencyMap.containsKey(rightChar)) {
                charFrequencyMap.put(rightChar, charFrequencyMap.get(rightChar) - 1);
                if (charFrequencyMap.get(rightChar) == 0) {
                    matched++;
                }
            }
            if (matched == charFrequencyMap.size()) {
                return true;
            }
            if (windowEnd >= pattern.length() - 1) {
                char leftChar = str.charAt(windowStart++);
                if (charFrequencyMap.containsKey(leftChar)) {
                    if (charFrequencyMap.get(leftChar) == 0) {
                        matched--;
                    }
                    charFrequencyMap.put(leftChar, charFrequencyMap.get(leftChar) + 1);
                }
            }
        }
        return false;
    }
}