Package g1401_1500.s1466_reorder_routes_to_make_all_paths_lead_to_the_city_zero

Class 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 Detail

      • Solution

        public Solution()

    • Method Detail

      • minReorder

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