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riddler_jan22.R

library("igraph")
library("stringi")
library("magrittr")


generate_bridge_df <- function(nrow, ncol) {
  this_layer <- generate_layer(ncol)
  first_connections <- data.frame(from = "Northside", 
                                  to = get_layer_vertices(this_layer))
  all_bridges <- rbind(first_connections, this_layer)
  
  for (row in seq(nrow - 1)) {
    current_vertices <- get_layer_vertices(this_layer)
    this_layer <- generate_layer(ncol)
    these_connections <- data.frame(from = current_vertices,
                                    to = get_layer_vertices(this_layer))
    all_bridges <- rbind(all_bridges, these_connections, this_layer)
  }
  
  last_connections <- data.frame(from = get_layer_vertices(this_layer), 
                                 to = "Southside")
  graph.data.frame(rbind(all_bridges, last_connections), directed = FALSE)
}

generate_layer <- function(ncol) {
  island_names <- stri_rand_strings(ncol, 10)
  data.frame(from = island_names[1:(ncol - 1)],
             to   = island_names[2:ncol],
             stringsAsFactors = FALSE)
}

get_layer_vertices <- function(layer) {
  unique(c(layer$to, layer$from))
}

random_storm <- function(island_graph) {
  bridges <- E(island_graph)
  destroyed_bridges <- bridges[runif(length(bridges)) > 0.5]
  delete_edges(island_graph, destroyed_bridges)
}

can_get_south <- function(island_graph) {
  vertex.connectivity(island_graph, "Northside", "Southside") > 0
}

unharmed_bridges <- generate_bridge_df(2, 3)
plot(unharmed_bridges)

unharmed_bridges %>% random_storm %>% plot
unharmed_bridges %>% random_storm %>% can_get_south