Alien Dictionary Leetcode

 

 

未完待续

public class Solution {
    public String alienOrder(String[] words) {
        HashMap<Character, ArrayList<Character>> hm = new HashMap<>();
        HashMap<Character, Integer> degree = new HashMap<>();
        for (int i = 0; i < words.length - 1; i++) {
            char[] first = words[i].toCharArray();
            char[] second = words[i + 1].toCharArray();
            int length = Math.min(first.length, second.length);
            for (int j = 0; j < length; j++) {
                if (first[j] != second[j]) {
                    if (!hm.containsKey(first[j])) {
                        hm.put(first[j], new ArrayList<>());
                    }
                    hm.get(first[j]).add(second[j]);
                    if (!hm.containsKey(second[j])) {
                        hm.put(second[j], new ArrayList<>());
                    }
                    if (!degree.containsKey(first[j])) {
                        degree.put(first[j], 0);
                    }
                    if (!degree.containsKey(second[j])) {
                        degree.put(second[j], 1);
                    } else {
                        degree.put(second[j], degree.get(second[j]) + 1);
                    }
                    break;
                } else {
                    if (!hm.containsKey(first[j])) {
                        hm.put(first[j], new ArrayList<>());
                    }
                    if (!degree.containsKey(first[j])) {
                        degree.put(first[j], 0);
                    }
                }
            }
            
        }
        Queue<Character> q = new LinkedList<>();
        for (Character c : degree.keySet()) {
            if (degree.get(c) == 0) {
                q.offer(c);
            }
        }
        StringBuilder res = new StringBuilder();
        while (!q.isEmpty()) {
            Character c = q.poll();
            ArrayList<Character> second = hm.get(c);
            for (int i = 0; i < second.size(); i++) {
                degree.put(second.get(i), degree.get(second.get(i)) - 1);
                if (degree.get(second.get(i)) == 0) {
                    q.offer(second.get(i));
                }
            }
            res.append(c);
        }
        if (res.length() != degree.size()) {
            return "";
        }
        return res.toString();
    }
}