Second Minimum Time to Reach Destination
Difficulty: Hard
Category: DSA
Topics: Breadth-First Search, Graph, Shortest Path
A city is represented as a **bi-directional connected** graph with `n` vertices where each vertex is labeled from `1` to `n` (**inclusive**). The edges in the graph are represented as a 2D integer array `edges`, where each `edges[i] = [ui, vi]` denotes a bi-directional edge between vertex `ui` and vertex `vi`. Every vertex pair is connected by **at most one** edge, and no vertex has an edge to itself. The time taken to traverse any edge is `time` minutes.
Each vertex has a traffic signal which changes its color from **green** to **red** and vice versa every `change` minutes. All signals change **at the same time**. You can enter a vertex at **any time**, but can leave a vertex **only when the signal is green**. You **cannot wait **at a vertex if the signal is **green**.
The **second minimum value** is defined as the smallest value** strictly larger **than the minimum value.
- For example the second minimum value of `[2, 3, 4]` is `3`, and the second minimum value of `[2, 2, 4]` is `4`.
Given `n`, `edges`, `time`, and `change`, return _the **second minimum time** it will take to go from vertex _`1`_ to vertex _`n`.
**Notes:**
- You can go through any vertex **any** number of times, **including** `1` and `n`.
- You can assume that when the journey **starts**, all signals have just turned **green**.
**Example 1:**
**Input:** n = 5, edges = [[1,2],[1,3],[1,4],[3,4],[4,5]], time = 3, change = 5
**Output:** 13
**Explanation:**
The figure on the left shows the given graph.
The blue path in the figure on the right is the minimum time path.
The time taken is:
- Start at 1, time elapsed=0
- 1 -> 4: 3 minutes, time elapsed=3
- 4 -> 5: 3 minutes, time elapsed=6
Hence the minimum time needed is 6 minutes.
The red path shows the path to get the second minimum time.
- Start at 1, time elapsed=0
- 1 -> 3: 3 minutes, time elapsed=3
- 3 -> 4: 3 minutes, time elapsed=6
- Wait at 4 for 4 minutes, time elapsed=10
- 4 -> 5: 3 minutes, time elapsed=13
Hence the second minimum time is 13 minutes.
```
**Example 2:**
**Input:** n = 2, edges = [[1,2]], time = 3, change = 2
**Output:** 11
**Explanation:**
The minimum time path is 1 -> 2 with time = 3 minutes.
The second minimum time path is 1 -> 2 -> 1 -> 2 with time = 11 minutes.
```
**Constraints:**
- `2 <= n <= 104`
- `n - 1 <= edges.length <= min(2 * 104, n * (n - 1) / 2)`
- `edges[i].length == 2`
- `1 <= ui, vi <= n`
- `ui != vi`
- There are no duplicate edges.
- Each vertex can be reached directly or indirectly from every other vertex.
- `1 <= time, change <= 103`