g1401_1500.s1466_reorder_routes_to_make_all_paths_lead_to_the_city_zero

Class Solution

java.lang.Object

g1401_1500.s1466_reorder_routes_to_make_all_paths_lead_to_the_city_zero.Solution

public class Solution
extends Object

1466 - Reorder Routes to Make All Paths Lead to the City Zero.

Medium

There are n cities numbered from 0 to n - 1 and n - 1 roads such that there is only one way to travel between two different cities (this network form a tree). Last year, The ministry of transport decided to orient the roads in one direction because they are too narrow.

Roads are represented by connections where connections[i] = [ai, bi] represents a road from city ai to city bi.

This year, there will be a big event in the capital (city 0), and many people want to travel to this city.

Your task consists of reorienting some roads such that each city can visit the city 0. Return the minimum number of edges changed.

It’s guaranteed that each city can reach city 0 after reorder.

Example 1:

Input: n = 6, connections = [[0,1],[1,3],[2,3],[4,0],[4,5]]

Output: 3

Explanation: Change the direction of edges show in red such that each node can reach the node 0 (capital).

Example 2:

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

Output: 2

Explanation: Change the direction of edges show in red such that each node can reach the node 0 (capital).

Example 3:

Input: n = 3, connections = [[1,0],[2,0]]

Output: 0

Constraints:

• 2 <= n <= 5 * 104
• connections.length == n - 1
• connections[i].length == 2
• 0 <= ai, bi <= n - 1
• ai != bi

Constructor Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
int	minReorder(int n, int[][] connections)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Solution

public Solution()

Method Detail

minReorder

public int minReorder(int n,
                      int[][] connections)