You are given two integers, n and threshold, as well as a directed weighted graph of n nodes numbered from 0 to n - 1. The graph is represented by a 2D integer array edges, where edges[i] = [Ai, Bi, Wi] indicates that there is an edge going from node Ai to node Bi with weight Wi.
You have to remove some edges from this graph (possibly none), so that it satisfies the following conditions:
threshold outgoing edges.Return the minimum possible value of the maximum edge weight after removing the necessary edges. If it is impossible for all conditions to be satisfied, return -1.
Example 1:
Input: n = 5, edges = [[1,0,1],[2,0,2],[3,0,1],[4,3,1],[2,1,1]], threshold = 2
Output: 1
Explanation:

Remove the edge 2 -> 0. The maximum weight among the remaining edges is 1.
Example 2:
Input: n = 5, edges = [[0,1,1],[0,2,2],[0,3,1],[0,4,1],[1,2,1],[1,4,1]], threshold = 1
Output: -1
Explanation:
It is impossible to reach node 0 from node 2.
Example 3:
Input: n = 5, edges = [[1,2,1],[1,3,3],[1,4,5],[2,3,2],[3,4,2],[4,0,1]], threshold = 1
Output: 2
Explanation:

Remove the edges 1 -> 3 and 1 -> 4. The maximum weight among the remaining edges is 2.
Example 4:
Input: n = 5, edges = [[1,2,1],[1,3,3],[1,4,5],[2,3,2],[4,0,1]], threshold = 1
Output: -1
Constraints:
2 <= n <= 1051 <= threshold <= n - 11 <= edges.length <= min(105, n * (n - 1) / 2).edges[i].length == 30 <= Ai, Bi < nAi != Bi1 <= Wi <= 106When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:
The goal is to find the smallest possible heaviest edge we can allow while still being able to connect all the locations. To do this the brute force strategy tries every possible weight limit until one works. For each limit, we check if it's possible to travel between all the locations using only roads with that weight or less.
Here's how the algorithm would work step-by-step:
def minimize_maximum_edge_weight_brute_force(number_of_locations, roads):
# Sort the edges by weight to make the guessing process easier.
roads.sort(key=lambda road: road[2])
for maximum_allowed_weight in range(1, 101): # Iterate through possible weights
accessible_roads = []
for start_location, end_location, road_weight in roads:
if road_weight <= maximum_allowed_weight:
accessible_roads.append((start_location, end_location))
# Check if all locations are connected with the current weight limit.
if is_graph_connected(number_of_locations, accessible_roads):
return maximum_allowed_weight
def is_graph_connected(number_of_locations, accessible_roads):
if number_of_locations == 0:
return True
if not accessible_roads and number_of_locations > 1:
return False
visited_locations = set()
queue = [1] # Start BFS from location 1
visited_locations.add(1)
while queue:
current_location = queue.pop(0)
for start_location, end_location in accessible_roads:
if start_location == current_location and end_location not in visited_locations:
queue.append(end_location)
visited_locations.add(end_location)
elif end_location == current_location and start_location not in visited_locations:
queue.append(start_location)
visited_locations.add(start_location)
# Ensure every location was visited.
return len(visited_locations) == number_of_locationsThe goal is to find the smallest possible maximum weight of an edge in a graph that can still connect all the nodes as specified. We use a binary search approach: we guess a maximum edge weight and see if we can build a connected graph with only edges of that weight or less. If so, we try a smaller weight; otherwise, we try a larger one.
Here's how the algorithm would work step-by-step:
def minimize_maximum_edge_weight(number_of_nodes, edges):
left = 0
right = max(edge[2] for edge in edges)
minimum_maximum_weight = right
while left <= right:
mid = (left + right) // 2
# Check if the graph is connected with the current maximum weight.
if is_connected(number_of_nodes, edges, mid):
minimum_maximum_weight = mid
right = mid - 1
else:
left = mid + 1
return minimum_maximum_weight
def is_connected(number_of_nodes, edges, max_weight):
adj = [[] for _ in range(number_of_nodes)]
for source, destination, weight in edges:
if weight <= max_weight:
adj[source - 1].append(destination - 1)
adj[destination - 1].append(source - 1)
visited = [False] * number_of_nodes
# Start DFS from node 0
dfs(0, adj, visited)
#If all nodes were visited, the graph is connected
return all(visited)
def dfs(node, adj, visited):
visited[node] = True
for neighbor in adj[node]:
if not visited[neighbor]:
dfs(neighbor, adj, visited)
# Example usage (This part is NOT part of the solution, just for testing)
if __name__ == '__main__':
number_of_nodes = 4
edges = [[1, 2, 3], [2, 3, 5], [3, 4, 7], [1, 4, 9]]
result = minimize_maximum_edge_weight(number_of_nodes, edges)
print(f"Minimum maximum edge weight: {result}")| Case | How to Handle |
|---|---|
| Empty graph (no edges) | Return 0 or infinity (depending on the problem's definition of 'minimum maximum weight') because there are no edges to consider. |
| Graph with a single node | Return 0 or infinity (depending on the problem's definition) because there are no edges. |
| Graph with two nodes and a single edge of weight 0 | Return 0 because the minimum maximum edge weight is 0 in this case. |
| Graph with many nodes and edges, all with the same weight | The minimum maximum edge weight will be that single weight. |
| Graph with edges that have extremely large weights, potentially leading to integer overflow | Use a data type (e.g., long) that can accommodate large values to avoid overflow during calculations, and be mindful of potential overflow in any weight comparisons. |
| Graph that is not connected | The behavior depends on the problem requirements; either return an error or consider only the connected component containing the start/end nodes, if those are specified. |
| Graph that contains a cycle | Algorithms such as binary search with Disjoint Set Union (DSU) work correctly with cycles because they consider all edges regardless of cycle presence. |
| No path exists between start and end nodes (if the problem asks for a path between nodes) | Return an appropriate error value (e.g., infinity or -1) to indicate that no valid path exists. |