add quick3 string

algs4/quick3_string.py

@@ -0,0 +1,72 @@
+"""
+   Execution:  python quick3_string.py < input.txt
+
+   Data files:   https://algs4.cs.princeton.edu/51radix/words3.txt
+
+   % python quick3_string.py < words3.txt
+   all
+   bad
+   bed
+   bug
+   dad
+   ...
+   yes
+   yet
+   zoo
+"""
+
+
+class Quick3string:
+    R = 256  # extended ASCII alphabet size
+    CUTOFF = 15  # cutoff to insertion sort
+
+    def __init__(self, a):
+        self.aux = ["" for _ in range(len(a))]
+        self.sort(a, 0, len(a)-1, 0)
+
+    def sort(self, a, lo, hi, d):
+        if hi <= lo + self.CUTOFF:
+            self.insertion(a, lo, hi, d)
+            return
+
+        lt, gt = lo, hi
+        v = self.char_at(a[lo], d)
+        i = lo + 1
+        while i <= gt:
+            t = self.char_at(a[i], d)
+            if t < v:
+                self.exch(a, lt, i)
+                lt += 1
+                i += 1
+            elif t > v:
+                self.exch(a, i, gt)
+                gt -= 1
+            else:
+                i += 1
+        self.sort(a, lo, lt-1, d)
+        if v >= 0:
+            self.sort(a, lt, gt, d+1)
+        self.sort(a, gt+1, hi, d)
+
+    def insertion(self, a, lo, hi, d):
+        for i in range(lo, hi+1):
+            j = i
+            while j > lo and a[j][d] < a[j-1][d]:
+                a[j], a[j-1] = a[j-1], a[j]
+                j -= 1
+
+    def char_at(self, s, d):
+        return ord(s[d])
+
+    def exch(self, a, i, j):
+        a[i], a[j] = a[j], a[i]
+
+
+if __name__ == '__main__':
+    import sys
+    words = []
+    for line in sys.stdin:
+        words.extend(line.split())
+    Quick3string(words)
+    for item in words:
+        print(item)