From 68571cffb21fbb88f77052dbf652d6528fd9f7d4 Mon Sep 17 00:00:00 2001
From: ahuigo <a132811@gmail.com>
Date: Mon, 11 Feb 2019 17:41:12 +0800
Subject: [PATCH] More Simple Kiss BinHeap

---
 trees/binheap.py | 65 +++++++++++++++++++++++-------------------------
 1 file changed, 31 insertions(+), 34 deletions(-)

diff --git a/trees/binheap.py b/trees/binheap.py
index df619bc..68cc532 100644
--- a/trees/binheap.py
+++ b/trees/binheap.py
@@ -7,58 +7,55 @@
 # this heap takes key value pairs, we will assume that the keys are integers
 class BinHeap:
     def __init__(self):
-        self.heapList = [0]
+        self.heapList = []
         self.currentSize = 0
 
-
     def buildHeap(self,alist):
-        i = len(alist) // 2
         self.currentSize = len(alist)
-        self.heapList = [0] + alist[:]
-        print(len(self.heapList), i)
-        while (i > 0):
-            print(self.heapList, i)
+        self.heapList = alist[:]
+
+        i = len(alist)//2 -1
+        while (i >= 0):
             self.percDown(i)
+            print(i, self.heapList)
             i = i - 1
-        print(self.heapList,i)
                         
     def percDown(self,i):
-        while (i * 2) <= self.currentSize:
-            mc = self.minChild(i)
-            if self.heapList[i] > self.heapList[mc]:
-                tmp = self.heapList[i]
-                self.heapList[i] = self.heapList[mc]
-                self.heapList[mc] = tmp
-            i = mc
-                
-    def minChild(self,i):
-        if i * 2 + 1 > self.currentSize:
-            return i * 2
-        else:
-            if self.heapList[i * 2] < self.heapList[i * 2 + 1]:
-                return i * 2
+        heapList = self.heapList
+        while True:
+            child = 2*i+1
+            if child >= self.currentSize:
+                break
+            if child+1<self.currentSize and heapList[child+1] < heapList[child]:
+                child += 1
+            if heapList[i] > heapList[child]:
+                # swap
+                heapList[i],heapList[child] = heapList[child],heapList[i] 
             else:
-                return i * 2 + 1
+                break
+            i = child
 
     def percUp(self,i):
-        while i // 2 > 0:
-            if self.heapList[i] < self.heapList[i//2]:
-               tmp = self.heapList[i // 2]
-               self.heapList[i // 2] = self.heapList[i]
-               self.heapList[i] = tmp
-            i = i // 2
- 
+        heapList = self.heapList
+        while (i-1) // 2 >= 0:
+            parent = (i-1)//2
+            if heapList[i] < heapList[parent]:
+                heapList[i], heapList[parent] = heapList[parent],heapList[i]
+            else:
+                break
+            i = parent
+
     def insert(self,k):
         self.heapList.append(k)
         self.currentSize = self.currentSize + 1
-        self.percUp(self.currentSize)
+        self.percUp(self.currentSize-1)
 
     def delMin(self):
-        retval = self.heapList[1]
-        self.heapList[1] = self.heapList[self.currentSize]
+        retval = self.heapList[0]
+        self.heapList[0] = self.heapList[self.currentSize-1]
         self.currentSize = self.currentSize - 1
         self.heapList.pop()
-        self.percDown(1)
+        self.percDown(0)
         return retval
         
     def isEmpty(self):