[数据结构与算法]1202. 交换字符串中的元素 并查集+排序

// 将同一个联通部分的字符拿出来, sort下
// 然后逐个填入....

class Solution {
    private int[] father;

    public int find(int x) {
        if (x == father[x])
            return x;
        return father[x] = find(father[x]);
    }

    public void union(int u, int v) {
        int x = find(u);
        int y = find(v);
        father[x] = y;
    }

    public String smallestStringWithSwaps(String s, List<List<Integer>> pairs) {
        int n = s.length();
        father = new int[n + 1];
        for (int i = 1; i <= n; i++)
            father[i] = i;

        for (List<Integer> x : pairs) {
            int u = x.get(0) + 1;
            int v = x.get(1) + 1;
            union(u, v);
        }

        for (int i = 1; i <= n; i++)
            find(i);

        HashMap<Integer, Integer> map = new HashMap<>();
        int cnt = 0;
        for (int i = 1; i <= n; i++) {
            if (!map.containsKey(father[i]))
                map.put(father[i], cnt++);
        }
        ArrayList<ArrayList<Character> > res = new ArrayList<>(cnt);
        for (int i = 0; i < cnt; i++)
            res.add(new ArrayList<>());
        ArrayList<Integer> index = new ArrayList<>(cnt);
        for (int i = 0; i < cnt; i++)
            index.add(0);
        for (int i = 1; i <= n; i++) {
            Integer x = map.get(father[i]);

            res.get(x).add(s.charAt(i - 1));
        }

        for (int i = 0; i < cnt; i++){
            Collections.sort(res.get(i));
        }

        StringBuilder sb = new StringBuilder(n);
        for (int i = 1; i <= n; i++) {
            int t = map.get(father[i]);
            sb.append(res.get(t).get(index.get(t)));
            index.set(t, index.get(t) + 1);
        }

        return sb.toString();
    }
}

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