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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0701_0800.s0761_special_binary_string;

// #Hard #String #Recursion #2022_03_25_Time_1_ms_(100.00%)_Space_40.2_MB_(86.57%)

import java.util.PriorityQueue;

/**
 * 761 - Special Binary String\.
 *
 * Hard
 *
 * **Special binary strings** are binary strings with the following two properties:
 *
 * *   The number of `0`'s is equal to the number of `1`'s.
 * *   Every prefix of the binary string has at least as many `1`'s as `0`'s.
 *
 * You are given a **special binary** string `s`.
 *
 * A move consists of choosing two consecutive, non-empty, special substrings of `s`, and swapping them. Two strings are consecutive if the last character of the first string is exactly one index before the first character of the second string.
 *
 * Return _the lexicographically largest resulting string possible after applying the mentioned operations on the string_.
 *
 * **Example 1:**
 *
 * **Input:** s = "11011000"
 *
 * **Output:** "11100100"
 *
 * **Explanation:**
 *
 *     The strings "10" [occuring at s[1]] and "1100" [at s[3]] are swapped.
 *     This is the lexicographically largest string possible after some number of swaps. 
 *
 * **Example 2:**
 *
 * **Input:** s = "10"
 *
 * **Output:** "10"
 *
 * **Constraints:**
 *
 * *   `1 <= s.length <= 50`
 * *   `s[i]` is either `'0'` or `'1'`.
 * *   `s` is a special binary string.
**/
public class Solution {
    public String makeLargestSpecial(String s) {
        if (s == null || s.length() == 0 || s.length() == 2) {
            return s;
        }
        PriorityQueue pq = new PriorityQueue<>((a, b) -> b.compareTo(a));
        int acc = 1;
        int prev = 0;
        for (int i = 1; i <= s.length(); i++) {
            if (acc == 0) {
                if (!(prev == 0 && i == s.length())) {
                    pq.add(makeLargestSpecial(s.substring(prev, i)));
                }
                prev = i;
            }
            if (i == s.length()) {
                break;
            }
            if (s.charAt(i) == '1') {
                acc++;
            } else {
                acc--;
            }
        }
        StringBuilder ans = new StringBuilder();
        while (!pq.isEmpty()) {
            ans.append(pq.poll());
        }
        if (ans.length() == 0) {
            ans.append('1');
            ans.append(makeLargestSpecial(s.substring(1, s.length() - 1)));
            ans.append('0');
        }
        return ans.toString();
    }
}