#@ root: the root of searched tree
#@ nodeToFind: the tree-node to be found
#@ path: the path from root to node
#@@
#@@ search tree referenced by root, and return the path
#@@ from root to node, if node not exist, path = []
#@@
def getPath(root, nodeToFind, path):
if ( None == root or None == nodeToFind):
return False
# case 1: current root == node, so insert to path
if root == nodeToFind:
path.insert(0, root)
return True
# search in left barch and right branch
bFindInLeft = False
bFindInRight = False
if root.left:
bFindInLeft = getPath(root.left, nodeToFind, path)
if False == bFindInLeft and root.right :
bFindInRight = getPath(root.right, nodeToFind, path)
# case 2: nodeToFind in subtree of root, insert root
if bFindInLeft or bFindInRight:
path.insert(0, root)
return True
return False
函數的功能是在root 表示的樹中查找nodeToFind 結點,若找到,則在返回的時候,將路徑結點加入到path中,關於樹的遍歷有三種,這裏我們使用後序遍歷,目的是在知道所有情況後,再對root進行處理,因爲當前的結點root應不應該加入到路徑path中,不僅跟當前的結點root有關,還跟它的子結點有關,也就是若當前結點就是要找的結點,那麼將當前結點加入是沒有問題的,但是即使當前結點不是要查找的結點,而其子樹中有查找結點時,當前結點也是要加入到路徑中去的。這樣就不用每次都將結點插入,條件不滿足時還要進行結點的pop。
def getClosetParent(root, node1, node2):
path1 = []; path2 = []
if None == root or None == node1 or None == node2:
return None
#get the path from root to node1 and node2
getPath(root, node1, path1)
getPath(root, node2, path2)
# find closet parent of node1 and node2
shorPathLen = min( len(path1), len(path2) )
for i in range(1, shorPathLen):
if path1[ i ] != path2[ i ] and \
path1[ i - 1 ] == path2[ i - 1 ]:
return path1[ i - 1 ]
return None
因爲在getPath函數裏,我們獲得的路徑是從root開始的,即root爲path列表的第一個結點,那麼我們就從root開始,一次比較,找到最後一個相等的,就是二者最近的公共祖先。