From b1889cbbbaaf10c82b52994002569de72163d4d3 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Fri, 4 Dec 2020 23:24:41 -0800
Subject: [PATCH] Add heap.

---
 heap.cr | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 heap.cr

diff --git a/heap.cr b/heap.cr
new file mode 100644
index 0000000..cc106b9
--- /dev/null
+++ b/heap.cr
@@ -0,0 +1,83 @@
+class Array(T)
+  def bubble_up(i, &cmp)
+    return if i >= size
+    while i != 0
+      j = (i-1)//2
+      break if yield self[i], self[j]
+      self[i], self[j] = self[j], self[i]
+      i = j
+    end
+  end
+
+  def percalate_down(i, &cmp)
+    while i*2+1 < size
+      j1, j2 = i*2+1, i*2+2
+      v1 = self[j1]
+      v2 = self[j2]?
+      if v2 && (yield v1, v2) && (yield self[i], v2)
+        self[j2], self[i] = self[i], v2
+        i = j2
+      elsif yield self[i], v1
+        self[j1], self[i] = self[i], v1
+        i = j1
+      else
+        break
+      end
+    end
+  end
+
+  def heapify(&cmp : T,T -> Bool)
+    size.times do |i|
+      i = size - i - 1
+      bubble_up(i, &cmp)
+    end
+    self
+  end
+
+  def heapify
+    heapify do |i,j|
+      i < j
+    end
+  end
+
+  def heap_push(v, &cmp : T,T -> Bool)
+    self << v
+    bubble_up(size - 1, &cmp)
+  end
+
+  def heap_push(v)
+    heap_push(v) do |i,j|
+      i < j
+    end
+  end
+
+  def heap_pop(&cmp : T,T -> Bool)
+    self[0], self[size-1] = self[size-1], self[0]
+    v = pop
+    percalate_down(0, &cmp)
+    v
+  end
+
+  def heap_pop
+    heap_pop do |i, j|
+      i < j
+    end
+  end
+
+  def is_heap?(&cmp : T,T -> Bool)
+    (size-1).times do |i|
+      i = size - i - 1
+      vi = self[i]
+      vp = self[(i-1)//2]
+      return false unless (yield self[i], self[(i-1)//2]) || vi == vp
+    end
+    return true
+  end
+
+  def is_heap?
+    is_heap? do |i,j|
+      i < j
+    end
+  end
+
+end