Added Multi Key Quick Sort

Sorts/MultiKeyQuickSort.js

@@ -0,0 +1,202 @@
+/**
+ * According to Wikipedia, Multi-key quicksort, also known as three-way radix
+ * quicksort, is an algorithm for sorting strings. This hybrid of quicksort and
+ * radix sort was originally suggested by P. Shackleton, as reported in one of
+ * C.A.R. Hoare's seminal papers on quicksort its modern incarnation was
+ * developed by Jon Bentley and Robert Sedgewick in the mid-1990s.The algorithm
+ * is designed to exploit the property that in many problems, strings tend to
+ * have shared prefixes.
+ *
+ * This current implement is actually translated from its Java counterpart based
+ * on the implementation by Nathan Fiedler in which the implementation was translated
+ * from C in the paper "Fast algorithms for sorting and searching strings" paper
+ * published in 1997.
+ *
+ *
+ * @author Jian Liew
+ */
+
+/**
+ * This function will sort the array in place.
+ *
+ * @param {*} The array of Strings to be sorted
+ *
+ */
+function multiKeyQuickSort(strings) {
+  if (strings != null && strings.length > 1) {
+    ssort(strings, 0, strings.length, 0);
+  }
+}
+
+function vecSwap(a, i, j, n) {
+  while (n-- > 0) {
+    const t = a[i];
+    a[i] = a[j];
+    a[j] = t;
+    i++;
+    j++;
+  }
+}
+
+function sort(strings, low, high, depth) {
+  if (
+    strings != null &&
+    strings.length > 1 &&
+    low >= 0 &&
+    low < high &&
+    depth >= 0
+  ) {
+    ssort(strings, low, high - low, depth);
+  }
+}
+
+function insertionSort(strings, low, high, depth) {
+  if (strings == null || low < 0 || high <= low || depth < 0) {
+    return;
+  }
+  for (let i = low + 1; i < high; i++) {
+    for (let j = i; j > low; j--) {
+      let idx = depth;
+      let s = idx < strings[j - 1].length ? strings[j - 1].charAt(idx) : 0;
+      let t = idx < strings[j].length ? strings[j].charAt(idx) : 0;
+      while (s == t && idx < strings[j - 1].length) {
+        idx++;
+        s = idx < strings[j - 1].length ? strings[j - 1].charAt(idx) : 0;
+        t = idx < strings[j].length ? strings[j].charAt(idx) : 0;
+      }
+      if (s <= t) {
+        break;
+      }
+      let tmp = strings[j];
+      strings[j] = strings[j - 1];
+      strings[j - 1] = tmp;
+    }
+  }
+}
+
+function ssort(a, base, n, depth) {
+  const THRESHOLD = 16;
+
+  if (n < THRESHOLD) {
+    insertionSort(a, base, base + n, depth);
+    return;
+  }
+  let pl = base;
+  let pm = base + n / 2;
+  let pn = base + n - 1;
+  let r;
+  if (n > 30) {
+    let d = n / 8;
+    pl = med3(a, base, base + d, base + 2 * d, depth);
+    pm = med3(a, base + n / 2 - d, pm, base + n / 2 + d, depth);
+    pn = med3(a, base + n - 1 - 2 * d, base + n - 1 - d, pn, depth);
+  }
+
+  pm = med3(a, pl, pm, pn, depth);
+  let t = a[base];
+  a[base] = a[pm];
+  a[pm] = t;
+  let v = charAt(a[base], depth);
+  let allzeros = v == 0;
+  let le = base + 1,
+    lt = le;
+  let gt = base + n - 1,
+    ge = gt;
+  while (true) {
+    for (; lt <= gt && (r = charAt(a[lt], depth) - v) <= 0; lt++) {
+      if (r == 0) {
+        t = a[le];
+        a[le] = a[lt];
+        a[lt] = t;
+        le++;
+      } else {
+        allzeros = false;
+      }
+    }
+    for (; lt <= gt && (r = charAt(a[gt], depth) - v) >= 0; gt--) {
+      if (r == 0) {
+        t = a[gt];
+        a[gt] = a[ge];
+        a[ge] = t;
+        ge--;
+      } else {
+        allzeros = false;
+      }
+    }
+    if (lt > gt) {
+      break;
+    }
+    t = a[lt];
+    a[lt] = a[gt];
+    a[gt] = t;
+    lt++;
+    gt--;
+  }
+  pn = base + n;
+  r = Math.min(le - base, lt - le);
+
+  vecSwap(a, base, lt - r, r);
+  r = Math.min(ge - gt, pn - ge - 1);
+  vecSwap(a, lt, pn - r, r);
+  if ((r = lt - le) > 1) {
+    ssort(a, base, r, depth);
+  }
+  if (!allzeros) {
+    ssort(a, base + r, le + n - ge - 1, depth + 1);
+  }
+  if ((r = ge - gt) > 1) {
+    ssort(a, base + n - r, r, depth);
+  }
+}
+
+function med3(a, l, m, h, depth) {
+  console.log(a, l, m, h, depth);
+  let va = charAt(a[l], depth);
+  let vb = charAt(a[m], depth);
+  if (va == vb) {
+    return l;
+  }
+  let vc = charAt(a[h], depth);
+  if (vc == va || vc == vb) {
+    return h;
+  }
+  return va < vb
+    ? vb < vc
+      ? m
+      : va < vc
+      ? h
+      : l
+    : vb > vc
+    ? m
+    : va < vc
+    ? l
+    : h;
+}
+
+function charAt(s, d) {
+  console.log(s);
+
+  return d < s.length ? s.charAt(d) : 0;
+}
+
+// Test case 1
+
+let unsortedArray = ['apple', 'cat', 'boy'];
+let sortedArray = ['apple', 'boy', 'cat'];
+
+multiKeyQuickSort(unsortedArray);
+console.log('observed:', unsortedArray, 'expected:', sortedArray);
+
+// Test case 2
+let unsortedArray2 = ['z', 'm', '', 'a', 'd', 'tt', 'tt', 'tt', 'foo', 'bar'];
+let sortedArray2 = ['', 'a', 'bar', 'd', 'foo', 'm', 'tt', 'tt', 'tt', 'z'];
+
+console.log('observed:', unsortedArray2, 'expected:', sortedArray2);
+multiKeyQuickSort(unsortedArray2);
+
+// Test Case 3
+let unsortedArray3 = ['aa', 'ad', 'ab', 'boy'];
+let sortedArray3 = ['aa', 'ab', 'ad', 'boy'];
+
+multiKeyQuickSort(unsortedArray3);
+console.log('observed:', unsortedArray3, 'expected:', sortedArray3);