You are given a data structure of employee information, which includes the employee's unique id, his importance value and his direct subordinates' id.

For example, employee 1 is the leader of employee 2, and employee 2 is the leader of employee 3. They have importance value 15, 10 and 5, respectively. Then employee 1 has a data structure like [1, 15, [2]], and employee 2 has [2, 10, [3]], and employee 3 has [3, 5, []]. Note that although employee 3 is also a subordinate of employee 1, the relationship is not direct.

Now given the employee information of a company, and an employee id, you need to return the total importance value of this employee and all his subordinates.

Example 1:

Input: [[1, 5, [2, 3]], [2, 3, []], [3, 3, []]], 1
Output: 11
Explanation:
Employee 1 has importance value 5, and he has two direct subordinates: employee 2 and employee 3. They both have importance value 3. So the total importance value of employee 1 is 5 + 3 + 3 = 11.

Note:

    1. One employee has at most one direct leader and may have several subordinates.
    2. The maximum number of employees won't exceed 2000.

这道题定义了一种员工类,有id,重要度,和direct report的员工,让我们求某个员工的总重要度。我们要明白的是就算某个员工不直接向你汇报工作,而是向你手下人汇报,这个人的重要度也会算进你的重要度中,想到了狗家的统计直接汇报个数系统就是这样的。这其实就是之前那道 Nested List Weight Sum 的变化形式,我们可以用DFS来做。首先我们想,为了快速的通过id来定位到员工类,需要建立一个id和员工类的映射,然后我们根据给定的员工id来算其重要度。计算方法当然是其本身的重要度加上其所有手下人的重要度,对于手下人,还要累加其手下人的重要度。需要注意的是,像这种类似有向图遍历的问题都需要用一个HashSet来记录访问过的结点,以免有环存在,从而陷入无限死循环。但是由于这道题的场景比较特殊,一个人是不可能给自己的下属汇报的,所以不会有环存在,我们也乐得省事。建立一个结果res变量,加上当前员工的重要度,然后遍历其所有手下,对其每个手下人调用递归函数加到res上,最后返回res即可,参见代码如下:

解法一:

class Solution {
public:
int getImportance(vector<Employee*> employees, int id) {
unordered_map<int, Employee*> m;
for (auto e : employees) m[e->id] = e;
return helper(id, m);
}
int helper(int id, unordered_map<int, Employee*>& m) {
int res = m[id]->importance;
for (int num : m[id]->subordinates) {
res += helper(num, m);
}
return res;
}
};

我们也可以用BFS来做,使用一个queue来辅助运算,开始将给定员工id放入,然后当queue不为空进行循环,每次取出队首员工,累加上当前员工的复杂度到结果res,然后将其所有手下人加入队列等待遍历,参见代码如下:

解法二:

class Solution {
public:
int getImportance(vector<Employee*> employees, int id) {
int res = ;
queue<int> q{{id}};
unordered_map<int, Employee*> m;
for (auto e : employees) m[e->id] = e;
while (!q.empty()) {
auto t = q.front(); q.pop();
res += m[t]->importance;
for (int num : m[t]->subordinates) {
q.push(num);
}
}
return res;
}
};

类似题目:

Nested List Weight Sum

参考资料:

https://leetcode.com/problems/employee-importance/

https://leetcode.com/problems/employee-importance/discuss/112587/Java-HashMap-bfs-dfs

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