767. 重构字符串

给定一个字符串S，检查是否能重新排布其中的字母，使得两相邻的字符不同。

若可行，输出任意可行的结果。若不可行，返回空字符串。

示例 1:

输入: S = "aab"
输出: "aba"
示例 2:

输入: S = "aaab"
输出: ""

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/reorganize-string
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Scanner;

class Solution {

    private int[] findTop2(int[] cnt) {
        PriorityQueue queue = new PriorityQueue<>(new Comparator() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return Integer.compare(cnt[o1], cnt[o2]);
            }
        });

        for (int i = 0; i < cnt.length; ++i) {
            if (cnt[i] != 0) {
                if (queue.size() != 2) {
                    queue.offer(i);
                } else {
                    if (cnt[queue.peek()] < cnt[i]) {
                        queue.poll();
                        queue.offer(i);
                    }
                }
            }
        }

        if (queue.size() == 2) {
            int left = queue.poll(), right = queue.poll();
            if (cnt[left] == cnt[right]) {
                return new int[]{Math.min(left, right), Math.max(left, right)};
            }
            return new int[]{right, left};
        } else {
            return new int[]{queue.poll(), -1};
        }
    }

    public String reorganizeString(String s) {
        int limit = s.length() / 2 + (s.length() & 1);
        int[] cnt = new int[26];
        for (int i = 0; i < s.length(); ++i) {
            cnt[s.charAt(i) - 'a']++;
            if (cnt[s.charAt(i) - 'a'] > limit) {
                return "";
            }
        }

        char[] ans = new char[s.length()];
        int index = 0;
        while (index < s.length()) {
            int[] top2 = findTop2(cnt);
            ans[index] = (char) (top2[0] + 'a');
            cnt[top2[0]]--;
            if (top2[1] != -1) {
                ans[index + 1] = (char) (top2[1] + 'a');
                cnt[top2[1]]--;
            }
            index += 2;
        }

        return new String(ans);
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            System.out.println(new Solution().reorganizeString(in.next()));
        }
    }
}