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deleted 902 characters in body

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edited Nov 13, 2018 at 15:31

4.3k
7
29

R, 117 63 6359 bytes

@Giuseppe with most of the bytes saved:

function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<=2^.5<2)<2)

Try it online!Try it online!

dist computes distances (default is Euclidean) among rows of a matrix. which with second argument TRUE returns the coordinates where the predicate is true.

Coordinates are neighbours if the distance between them is not more than the square root of 2, but the inner <2 is good enough because the possible distance jumps from sqrt(2) ro 2.

Original:

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)

R, 117 63 bytes

@Giuseppe with most of the bytes saved:

function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<=2^.5)<2)

dist computes distances (default is Euclidean) among rows of a matrix. which with second argument TRUE returns the coordinates where the predicate is true. Coordinates are neighbours if the distance between them is not more than the square root of 2.

Original:

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)

R, 117 63 59 bytes

function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<2)<2)

dist computes distances (default is Euclidean) among rows of a matrix. which with second argument TRUE returns the coordinates where the predicate is true.

Coordinates are neighbours if the distance between them is not more than the square root of 2, but the inner <2 is good enough because the possible distance jumps from sqrt(2) ro 2.

added 316 characters in body

Source Link

edited Nov 12, 2018 at 20:25

4.3k
7
29

R, 117 63 bytes

@Giuseppe with most of the bytes saved:

function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<=2^.5)<2)

dist computes distances (default is Euclidean) among rows of a matrix. which with second argument TRUE returns the coordinates where the predicate is true. Coordinates are neighbours if the distance between them is not more than the square root of 2.

Original:

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)

R, 117 63 bytes

function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<=2^.5)<2)

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)

R, 117 63 bytes

@Giuseppe with most of the bytes saved:

function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<=2^.5)<2)

dist computes distances (default is Euclidean) among rows of a matrix. which with second argument TRUE returns the coordinates where the predicate is true. Coordinates are neighbours if the distance between them is not more than the square root of 2.

Original:

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)

added 402 characters in body

Source Link

edited Nov 12, 2018 at 17:22

4.3k
7
29

R, 117117 63 bytes

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrowcolSums(p)),functionas.matrix(y)sumdist(applywhich(p,1m==8,function(x)all((c(y-x)^2<2)T)))<=2^.5)==1<2)

A not-that-great explanation:Try it online!

f <- function(m) {
  p <- which,p=which(m == 8m==8, T)    # Matrix with rows of indices where 8 appears
  )sum(
    sapply(
      split(p, 1:nrow(p)), # Split p into a list of its rows
      function(y) {
        # 1 if no neighboring 8s, 0 otherwise
        sum(apply(p, 1, function(x) all((c(y - x)^2 < 2^2<2)))) == 1
      }
    )
  ==1)    
}

R, 117 bytes

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)

A not-that-great explanation:

f <- function(m) {
  p <- which(m == 8, T)    # Matrix with rows of indices where 8 appears
  sum(
    sapply(
      split(p, 1:nrow(p)), # Split p into a list of its rows
      function(y) {
        # 1 if no neighboring 8s, 0 otherwise
        sum(apply(p, 1, function(x) all((c(y - x)^2 < 2)))) == 1
      }
    )
  )    
}

R, 117 63 bytes

function(m)sum(colSums(as.matrix(dist(which(m==8,T)))<=2^.5)<2)

function(m,p=which(m==8,T))sum(sapply(split(p,1:nrow(p)),function(y)sum(apply(p,1,function(x)all((c(y-x)^2<2)))))==1)

Source Link

created Nov 12, 2018 at 16:18

4.3k
7
29

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