Skipping permutations

[arve0]

Hi!
In some problems, skipping permutations that does not solve the problem is an effective optimization. Would it be possible to add skipping of permutations?

Example:

for (let perm of G.permutations([1,2,3,4,5])) {
  if (shouldSkip(perm)) {
    // "increments" element at position 1
    G.incrementElement(1);
    // given perm == [1, 2, 3, 4, 5], 
    // 2 is at index 1,
    // next permutations will be [1, 3, 2, 4, 5]
  }
  if (isSolution(perm)) {
    break;
  }
}

function shouldSkip (perm) {
  // we know somehow that any permutations starting
  // with 1 and 2 will not solve the problem
  // e.g. none of these will solve the problem: [1,2,3,4,5], [1,2,3,4,5], [1,2,4,3,5] ....
  return perm[0] === 1 && perm[1] === 2;
}

PS: I've not looked into the code, but will take a grab at it if this sounds like a reasonable addition.

[arve0]

An example using the generator for signaling:

let generator = G.permutations([1,2,3,4,5]);

let v = generator.next();
while (!v.done) {
  let perm = v.value;
  if (shouldSkip(perm)) {
    // "increments" element at position 1
    v = generator.next(1);
    // given perm == [1, 2, 3, 4, 5], 
    // 2 is at index 1,
    // next permutations will be [1, 3, 2, 4, 5]
    continue;
  }
  if (isSolution(perm)) {
    break;
  }
  v = generator.next(); // get next permutation
}