Day10-Adapter_Array

Adapters <- read.table("day10.csv")
Adapters <- as.vector(Adapters[,1])

Nodes <- c(0, Adapters, max(Adapters)+3) # Insert begin 0 and ending +3

# PART 1: How much is the amount of Jumps 1 x Jumps 3 ?
Nodes <- sort(Nodes)
Jumps <- diff(Nodes)
table(Jumps)
table(Jumps)[1] * table(Jumps)[2]

# PART 2: How many different arrangements are possible?

# Counts occurrences in the seq of differences(Jumps)
J <- Jumps[1] # First difference value
S <- NULL     # size of the sequence of same differences
S_temp <- 1
for (k in 2:length(Jumps)) {
    if (Jumps[k]==Jumps[k-1]) {
        S_temp <- S_temp+1
    } else {
        S <- c(S, S_temp)
        J <- c(J, Jumps[k])
        S_temp <- 1
    }
}
S[length(S)+1] <- S_temp # fills last info of repeated differences

max(S) #max sequence is 5 (max diff=1 is of 4)

# Sequences of differences of 1 unit:
# For 1 difference -> 1 possibility (313 -> no variation: AB)
# For 2 differences -> 2 possibilities (3113 -> removes middle number: ex. ABC, AC)
# For 3 differences -> 4 possibilities (31113: ABCD, ACD, ABD, AD)
# For 4 differences -> 7 possibilities (311113: ABCDE, ACDE, ABDE, ABCE, ADE, ACE, ABE)

P <- rep(NA, length(S))
for (i in 1:length(S)) {
    if(J[i]==1 & S[i]==4) {
        P[i] = 7
    } else {
    if(J[i]==1 & S[i]==3) {
        P[i] = 4
    } else {
    if(J[i]==1 & S[i]==2) {
        P[i] = 2
    } else {
        P[i] = 1
    } } }
}
P #Sequence of possibilities
prod(P) # Product = 74049191673856