Minimum Window Substring LeetCode solution in Java

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class Solution {
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  public String minWindow(String s, String t) {
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    HashMap<Character, Integer> child = new HashMap<>();
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    HashMap<Character, Integer> parent = new HashMap<>();
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    int left = -1, right = -1, match = 0;
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    String window = "";
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    for (int i = 0; i < t.length(); i++) {
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      char c = t.charAt(i);
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      child.put(c, child.getOrDefault(c, 0) + 1); // Child frequency map
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    }
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    while (true) {
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      boolean f1 = false, f2 = false;
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      while (right < s.length() - 1 && match < t.length()) {
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        right++;
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        char c = s.charAt(right);
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        parent.put(c, parent.getOrDefault(c, 0) + 1); // Acquiring characters till
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        if (parent.getOrDefault(c, 0) <= child.getOrDefault(c, 0)) // match count is equal
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        match++;
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        f1 = true;
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      }
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      while (left < right && match == t.length()) {
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        String potstring = s.substring(left + 1, right + 1);
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        if (window.length() == 0 || window.length() > potstring.length())
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          window = potstring; // Calculating length of window
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        left++;
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        char c = s.charAt(left);
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        parent.put(c, parent.getOrDefault(c, 0) - 1);
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        if (parent.get(c) == 0) // Releasing characters by
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        parent.remove(c); // left pointer for finding smallest window
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        if (parent.getOrDefault(c, 0) < child.getOrDefault(c, 0)) match--;
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        f2 = true;
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      }
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      if (f1 == false && f2 == false) break;
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    }
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    return window;
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  }
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}