LeetCode in Kotlin

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

class Solution {
    private lateinit var graph: Array<IntArray?>
    private lateinit var suspicious: BooleanArray
    private lateinit var visited: BooleanArray

    fun remainingMethods(n: Int, k: Int, invocations: Array<IntArray>): List<Int> {
        pack(invocations, n)
        suspicious = BooleanArray(n)
        visited = BooleanArray(n)
        dfs(k, true)
        visited.fill(false)
        for (i in 0 until n) {
            if (!suspicious[i] && dfs2(i)) {
                visited.fill(false)
                dfs(k, false)
                break
            }
        }
        val rst = ArrayList<Int>()
        for (i in 0 until n) {
            if (!suspicious[i]) {
                rst.add(i)
            }
        }
        return rst
    }

    fun dfs(u: Int, sus: Boolean) {
        if (visited[u]) {
            return
        }
        visited[u] = true
        suspicious[u] = sus
        for (v in graph[u]!!) {
            dfs(v, sus)
        }
    }

    fun dfs2(u: Int): Boolean {
        if (suspicious[u]) {
            return true
        }
        if (visited[u]) {
            return false
        }
        visited[u] = true
        for (v in graph[u]!!) {
            if (dfs2(v)) {
                return true
            }
        }
        return false
    }

    private fun pack(edges: Array<IntArray>, n: Int) {
        val adj = IntArray(n)
        for (edge in edges) {
            adj[edge[0]]++
        }
        graph = arrayOfNulls<IntArray>(n)
        for (i in 0 until n) {
            graph[i] = IntArray(adj[i])
        }
        for (edge in edges) {
            graph[edge[0]]!![--adj[edge[0]]] = edge[1]
        }
    }
}

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