草稿-TANTAN

缓存与数据库数据一致性问题，可以先更新数据库之后解析数据库的BINLOG更新缓存 : 

博文：https://blog.csdn.net/striveb/article/details/95110502

binlog解析工具：https://github.com/javartisan/open-replicator

 MYSQL数据库的binlog格式：https://dev.mysql.com/doc/internals/en/event-meanings.html

共同好友问题 ：每一个用户维护一个关注set与被关注set，每次添加关注时候计算一下是否是共同好友，如果是的话，添加到共同好友列表中。

 https://segmentfault.com/q/1010000000501071

 https://www.jb51.net/article/54774.htm

import java.util.ArrayList;
import java.util.List;

class Test {

    public List<String> random(int[] nums, int cnt, boolean isPaiLie) {
        List<String> an = new ArrayList<>();
        StringBuilder sb = new StringBuilder();
        byte[] mtx = new byte[nums.length];
        if (isPaiLie)
            random(nums, mtx, cnt, an, sb);
        else
            random(nums, mtx, cnt, an, sb, 0);
        return an;
    }

    public void random(int[] nums, byte[] mtx, int cnt, List<String> list, StringBuilder sb) {

        if (cnt == 0) {
            list.add(sb.toString());
        }

        for (int i = 0; i < nums.length; i++) {
            if (mtx[i] == 1)
                continue;
            mtx[i] = 1;
            String str = nums[i] + ";";
            sb.append(str);
            cnt--;
            random(nums, mtx, cnt, list, sb);
            cnt++;
            sb.delete(sb.length() - str.length(), sb.length());
            mtx[i] = 0;
        }
    }

    public void random(int[] nums, byte[] mtx, int cnt, List<String> list, StringBuilder sb, int index) {

        if (cnt == 0) {
            list.add(sb.toString());
        }

        for (int i = index; i < nums.length; i++) {
            if (mtx[i] == 1)
                continue;
            mtx[i] = 1;
            String str = nums[i] + ";";
            sb.append(str);
            cnt--;
            random(nums, mtx, cnt, list, sb, i);
            cnt++;
            sb.delete(sb.length() - str.length(), sb.length());
            mtx[i] = 0;
        }
    }

    public static void main(String[] args) {
        System.out.println(new Test().random(new int[]{-2, 1, 3}, 2, false));
    }

}