Find virus originator

virusOriginator.swift

let graphNodes = [(1, 2), (2, 3), (2, 4), (4, 5), (4, 6), (5, 4)]

var nodeToIncomingEdgesCountMapping: [Int: Int] = [:]

for node in graphNodes {
    if nodeToIncomingEdgesCountMapping[node.0] == nil {
        nodeToIncomingEdgesCountMapping[node.0] = 0
    }
    
    if nodeToIncomingEdgesCountMapping[node.1] == nil {
        nodeToIncomingEdgesCountMapping[node.1] = 0
    }
    nodeToIncomingEdgesCountMapping[node.1]! += 1
}

for (node, incomingEdgesCount) in nodeToIncomingEdgesCountMapping {
    if incomingEdgesCount == 0 {
        print("Node is \(node)")
    }
}

print statement should read,
print("The node where the virus originated is \(node)")