27. Dijkstra's Algorithm

Hard

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Example 1:

Input: times = [[2,1,1],[2,3,1],[3,4,1]], n = 4, k = 2

Output: 2

Explanation: The signal starts at node 2. It takes 1 unit of time to reach node 1, 1 unit of time to reach node 3, and then 1 additional unit of time to reach node 4 from node 3. The maximum time to reach all nodes is 2.

Example 2:

Input: times = [[1,2,1]], n = 2, k = 1

Output: 1

Explanation: The signal starts at node 1. It takes 1 unit of time to reach node 2. Since there are only two nodes, the total time is 1.

Example 3:

Input: times = [[1,2,1]], n = 2, k = 2

Output: -1

Explanation: The signal starts at node 2. It can only reach itself, but node 1 is unreachable. Therefore, the result is -1.

Constraints:

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Time Complexity

O((V+E) log V)

Space Complexity

O(V)