Projektstart

backend/node_modules/obliterator/permutations.js

@@ -0,0 +1,94 @@
+/**
+ * Obliterator Permutations Function
+ * ==================================
+ *
+ * Iterator returning permutations of the given array.
+ */
+var Iterator = require('./iterator.js');
+
+/**
+ * Helper mapping indices to items.
+ */
+function indicesToItems(target, items, indices, r) {
+  for (var i = 0; i < r; i++) target[i] = items[indices[i]];
+}
+
+/**
+ * Permutations.
+ *
+ * @param  {array}    array - Target array.
+ * @param  {number}   r     - Size of the subsequences.
+ * @return {Iterator}
+ */
+module.exports = function permutations(array, r) {
+  if (!Array.isArray(array))
+    throw new Error(
+      'obliterator/permutations: first argument should be an array.'
+    );
+
+  var n = array.length;
+
+  if (arguments.length < 2) r = n;
+
+  if (typeof r !== 'number')
+    throw new Error(
+      'obliterator/permutations: second argument should be omitted or a number.'
+    );
+
+  if (r > n)
+    throw new Error(
+      'obliterator/permutations: the size of the subsequences should not exceed the length of the array.'
+    );
+
+  var indices = new Uint32Array(n),
+    subsequence = new Array(r),
+    cycles = new Uint32Array(r),
+    first = true,
+    i;
+
+  for (i = 0; i < n; i++) {
+    indices[i] = i;
+
+    if (i < r) cycles[i] = n - i;
+  }
+
+  i = r;
+
+  return new Iterator(function next() {
+    if (first) {
+      first = false;
+      indicesToItems(subsequence, array, indices, r);
+      return {value: subsequence, done: false};
+    }
+
+    var tmp, j;
+
+    i--;
+
+    if (i < 0) return {done: true};
+
+    cycles[i]--;
+
+    if (cycles[i] === 0) {
+      tmp = indices[i];
+
+      for (j = i; j < n - 1; j++) indices[j] = indices[j + 1];
+
+      indices[n - 1] = tmp;
+
+      cycles[i] = n - i;
+      return next();
+    } else {
+      j = cycles[i];
+      tmp = indices[i];
+
+      indices[i] = indices[n - j];
+      indices[n - j] = tmp;
+
+      i = r;
+
+      indicesToItems(subsequence, array, indices, r);
+      return {value: subsequence, done: false};
+    }
+  });
+};