杀掉进程

/*
题目思路:
1. 使用流构建进程树。
2. 使用递归方式杀掉进程及其子进程。
*/
import java.util.*;
import java.util.stream.Collectors;
 
public class KillProcessStream {
    public List<Integer> killProcess(List<Integer> pid, List<Integer> ppid, int kill) {
        Map<Integer, List<Integer>> processTree = ppid.stream().distinct().collect(Collectors.toMap(
            p -> p,
            p -> pid.stream().filter(id -> ppid.get(pid.indexOf(id)).equals(p)).collect(Collectors.toList())
        ));
        List<Integer> result = new ArrayList<>();
        killAllChildren(processTree, kill, result);
        return result;
    }
 
    private void killAllChildren(Map<Integer, List<Integer>> processTree, int kill, List<Integer> result) {
        result.add(kill);
        if (processTree.containsKey(kill)) {
            processTree.get(kill).forEach(child -> killAllChildren(processTree, child, result));
        }
    }
}