Finding groups in a single-dimensional grid array

Question

If I have a randomly generated array with 60 items (represented as 6x10) of 6 types (represented as integers 0-5), how can I search for groups of the same type within the array? (Vertically/horizontally connected groups of at least 3.)

I'm working in a scripting environment (LSL) similar to C++ and C.

Answer 1

Here is a parametrized working javascript example with comments, the trick is to use an array to denote the cells / nodes you have already visited.

var arr = [], visited, grp, val, rowLength = 6, threshold = 3;

// generate random array
for (var i = 0; i < 60; i++) {
  arr.push(Math.floor(Math.random() * 6));
}

alert(JSON.stringify(findGroups())); // executing the function and displaying the result.

function findGroups() {
  visited = []; // resetting visited
  var ret = []; // the return value is an array of groups
  for (var i = 0; i < arr.length; i++) {
    if (!visited[i]) {
      val = arr[i]; // set the value we are currently inspecting
      grp = []; // reset the current group
      flood(i); // the recursive flood function
      if (grp.length >= threshold) // add the group to the result if it meets the criteria 
        ret.push(grp);
    }
  }
  return ret;
}

function flood(idx) {
  if (visited[idx] || arr[idx] != val) // only look at cells with matching value...  
    return; // ... that weren't visited yet
  visited[idx] = true; // mark as visited
  grp.push(idx); // add index to current group
  if (idx % rowLength != 0) // can go left
    flood(idx - 1);
  if (idx % rowLength != rowLength - 1) // can go right
    flood(idx + 1);
  if (idx >= rowLength) // can go up
    flood(idx - rowLength);
  if (idx < arr.length - rowLength) // can go down
    flood(idx + rowLength);
}