Alice and Bob have an undirected graph of n nodes and three types of edges:Type 1: Can be traversed by Alice only.Type 2: Can be traversed by Bob only.Type 3: Can be traversed by both Alice and Bob.Given an array edges where edges[i] = [typei, ui, vi] represents a bidirectional edge of type typei between nodes ui and vi, find the maximum number of edges you can remove so that after removing the edges, the graph can still be fully traversed by both Alice and Bob. The graph is fully traversed by Alice and Bob if starting from any node, they can reach all other nodes.Return the maximum number of edges you can remove, or return -1 if Alice and Bob cannot fully traverse the graph. Example 1:Input: n = 4, edges = [[3,1,2],[3,2,3],[1,1,3],[1,2,4],[1,1,2],[2,3,4]]Output: 2Explanation: If we remove the 2 edges [1,1,2] and [1,1,3]. The graph will still be fully traversable by Alice and Bob. Removing any additional edge will not make it so. So the maximum number of edges we can remove is 2.Example 2:Input: n = 4, edges = [[3,1,2],[3,2,3],[1,1,4],[2,1,4]]Output: 0Explanation: Notice that removing any edge will not make the graph fully traversable by Alice and Bob.Example 3:Input: n = 4, edges = [[3,2,3],[1,1,2],[2,3,4]]Output: -1Explanation: In the current graph, Alice cannot reach node 4 from the other nodes. Likewise, Bob cannot reach 1. Therefore it's impossible to make the graph fully traversable. Constraints:1 <= n <= 1051 <= edges.length <= min(105, 3 * n * (n - 1) / 2)edges[i].length == 31 <= typei <= 31 <= ui < vi <= nAll tuples (typei, ui, vi) are distinct.
Question
Alice and Bob have an undirected graph of n nodes and three types of edges:Type 1: Can be traversed by Alice only.Type 2: Can be traversed by Bob only.Type 3: Can be traversed by both Alice and Bob.Given an array edges where edges[i] = [typei, ui, vi] represents a bidirectional edge of type typei between nodes ui and vi, find the maximum number of edges you can remove so that after removing the edges, the graph can still be fully traversed by both Alice and Bob. The graph is fully traversed by Alice and Bob if starting from any node, they can reach all other nodes.Return the maximum number of edges you can remove, or return -1 if Alice and Bob cannot fully traverse the graph. Example 1:Input: n = 4, edges = [[3,1,2],[3,2,3],[1,1,3],[1,2,4],[1,1,2],[2,3,4]]Output: 2Explanation: If we remove the 2 edges [1,1,2] and [1,1,3]. The graph will still be fully traversable by Alice and Bob. Removing any additional edge will not make it so. So the maximum number of edges we can remove is 2.Example 2:Input: n = 4, edges = [[3,1,2],[3,2,3],[1,1,4],[2,1,4]]Output: 0Explanation: Notice that removing any edge will not make the graph fully traversable by Alice and Bob.Example 3:Input: n = 4, edges = [[3,2,3],[1,1,2],[2,3,4]]Output: -1Explanation: In the current graph, Alice cannot reach node 4 from the other nodes. Likewise, Bob cannot reach 1. Therefore it's impossible to make the graph fully traversable. Constraints:1 <= n <= 1051 <= edges.length <= min(105, 3 * n * (n - 1) / 2)edges[i].length == 31 <= typei <= 31 <= ui < vi <= nAll tuples (typei, ui, vi) are distinct.
Solution
This problem can be solved using the Union-Find data structure. Here are the steps to solve this problem:
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First, sort the edges based on their types. Type 3 edges should be processed first because they can be traversed by both Alice and Bob.
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Initialize three variables,
cnt1,cnt2, andcnt3to keep track of the number of edges of each type. Also, initialize two Union-Find sets,uf1anduf2. -
For each edge of type 3, if the two nodes of the edge are not connected in
uf1(oruf2), union them and increasecnt3by 1. -
For each edge of type 1, if the two nodes of the edge are not connected in
uf1, union them and increasecnt1by 1. -
Repeat step 4 for edges of type 2, but use
uf2and increasecnt2. -
If all nodes are connected in both
uf1anduf2, return the total number of edges minuscnt1,cnt2, andcnt3. Otherwise, return -1.
This algorithm works because it tries to maximize the number of edges to remove while ensuring that the graph can still be fully traversed by both Alice and Bob. It processes type 3 edges first because they are more "valuable" as they can be traversed by both Alice and Bob. Then it processes type 1 and type 2 edges to connect the remaining nodes. If all nodes are connected in the end, it means the graph can be fully traversed by both Alice and Bob. The number of edges to remove is the total number of edges minus the number of edges used to connect all nodes.
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