Partially implement a Heap

Defining the insert (or "siftup") function described in the "Programming Pearls"
book.

scratch/facebook/heap.py

@@ -0,0 +1,30 @@
+from math import floor
+
+class Heap(object):
+    def __init__(self):
+        self.xs = [None]
+        self.i = 1
+
+    def __repr__(self):
+        return "[{}]".format(", ".join(str(x) for x in self.xs[1:]))
+
+    def insert(self, x):
+        if len(self.xs) == 1:
+            self.xs.append(x)
+            self.i += 1
+            return
+        self.xs.append(x)
+        i = self.i
+        while i != 1 and self.xs[floor(i / 2)] > self.xs[i]:
+            self.xs[floor(i / 2)], self.xs[i] = self.xs[i], self.xs[floor(i / 2)]
+            i = floor(i / 2)
+        self.i += 1
+
+    def root(self):
+        return self.xs[1]
+
+xs = Heap()
+print(xs)
+for x in [12, 15, 14, 21, 1, 10]:
+    xs.insert(x)
+    print(xs)