LeetCode-in-Java

3310. Remove Methods From Project

Medium

You are maintaining a project that has n methods numbered from 0 to n - 1.

You are given two integers n and k, and a 2D integer array invocations, where invocations[i] = [a_i, b_i] indicates that method a_i invokes method b_i.

There is a known bug in method k. Method k, along with any method invoked by it, either directly or indirectly, are considered suspicious and we aim to remove them.

A group of methods can only be removed if no method outside the group invokes any methods within it.

Return an array containing all the remaining methods after removing all the suspicious methods. You may return the answer in any order. If it is not possible to remove all the suspicious methods, none should be removed.

Example 1:

Input: n = 4, k = 1, invocations = [[1,2],[0,1],[3,2]]

Output: [0,1,2,3]

Explanation:

Method 2 and method 1 are suspicious, but they are directly invoked by methods 3 and 0, which are not suspicious. We return all elements without removing anything.

Example 2:

Input: n = 5, k = 0, invocations = [[1,2],[0,2],[0,1],[3,4]]

Output: [3,4]

Explanation:

Methods 0, 1, and 2 are suspicious and they are not directly invoked by any other method. We can remove them.

Example 3:

Input: n = 3, k = 2, invocations = [[1,2],[0,1],[2,0]]

Output: []

Explanation:

All methods are suspicious. We can remove them.

Constraints:

1 <= n <= 10⁵
0 <= k <= n - 1
0 <= invocations.length <= 2 * 10⁵
invocations[i] == [a_i, b_i]
0 <= a_i, b_i <= n - 1
a_i != b_i
invocations[i] != invocations[j]

Solution

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

public class Solution {
    private int[][] graph;
    private boolean[] suspicious;
    private boolean[] visited;

    public List<Integer> remainingMethods(int n, int k, int[][] invocations) {
        pack(invocations, n);
        suspicious = new boolean[n];
        visited = new boolean[n];
        dfs(k, true);
        Arrays.fill(visited, false);
        for (int i = 0; i < n; i++) {
            if (!suspicious[i] && dfs2(i)) {
                Arrays.fill(visited, false);
                dfs(k, false);
                break;
            }
        }
        ArrayList<Integer> rst = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            if (!suspicious[i]) {
                rst.add(i);
            }
        }
        return rst;
    }

    public void dfs(int u, boolean sus) {
        if (visited[u]) {
            return;
        }
        visited[u] = true;
        suspicious[u] = sus;
        for (int v : graph[u]) {
            dfs(v, sus);
        }
    }

    public boolean dfs2(int u) {
        if (suspicious[u]) {
            return true;
        }
        if (visited[u]) {
            return false;
        }
        visited[u] = true;
        for (int v : graph[u]) {
            if (dfs2(v)) {
                return true;
            }
        }
        return false;
    }

    private void pack(int[][] edges, int n) {
        int[] adj = new int[n];
        for (int[] edge : edges) {
            adj[edge[0]]++;
        }
        graph = new int[n][];
        for (int i = 0; i < n; i++) {
            graph[i] = new int[adj[i]];
        }
        for (int[] edge : edges) {
            graph[edge[0]][--adj[edge[0]]] = edge[1];
        }
    }
}

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