https://leetcode.com/problems/network-delay-time/

Solution.swift

class Solution {
    func networkDelayTime(_ times: [[Int]], _ n: Int, _ k: Int) -> Int {
        var graph: [Int: [(Int, Int)]] = [:]
        for time in times {
            var edges = graph[time[0]] ?? []
            edges.append((time[1], time[2]))
            graph[time[0]] = edges
        }

        struct HeapNode: Comparable {
            let n: Int
            let t: Int
            static func < (l: Self, r: Self) -> Bool { l.t < r.t }
        }

        var nodeTimes: [Int] = .init(repeating: Int.max, count: n+1) // indexing starts from 1 in the conditions
        var nodesLeft = n
        var heap: Heap<HeapNode> = [.init(n: k, t: 0)]

        while let node = heap.popMin() {
            if nodeTimes[node.n] == Int.max {
                nodesLeft -= 1
                if nodesLeft == 0 { return node.t }
            }
            nodeTimes[node.n] = node.t

            guard let edges = graph[node.n] else { continue }
            for e in edges {
                let t = node.t+e.1
                if nodeTimes[e.0] > t {
                    heap.insert(.init(n: e.0, t: t))
                }
            }
        }
        return -1
    }
}