Finding the inorder predecessor and iorder successor of a given node

Author: OmkarPathak

Trees/P05_InorderPredecessorAndSuccessor.py

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+# Author: OMKAR PATHAK
+
+# Input: root node, key
+#
+# Output: predecessor node, successor node
+# 1. If root is NULL
+#       then return
+# 2. if key is found then
+#     a. If its left subtree is not null
+#         Then predecessor will be the right most
+#         child of left subtree or left child itself.
+#     b. If its right subtree is not null
+#         The successor will be the left most child
+#         of right subtree or right child itself.
+#     return
+# 3. If key is smaller then root node
+#         set the successor as root
+#         search recursively into left subtree
+#     else
+#         set the predecessor as root
+#         search recursively into right subtree
+
+# Python program to find predecessor and successor in a BST
+
+# A BST node
+class Node(object):
+    # Constructor to create a new node
+    def __init__(self, data):
+        self.data  = data
+        self.left = None
+        self.right = None
+
+    # for finding the predecessor and successor of the node
+    def findPredecessorAndSuccessor(self, data):
+        global predecessor, successor
+        predecessor = None
+        successor = None
+
+        if self is None:
+            return
+
+        # if the data is in the root itself
+        if self.data == data:
+            # the maximum value in the left subtree is the predecessor
+            if self.left is not None:
+                temp = self.left
+                if temp.right is not None:
+                    while(temp.right):
+                        temp = temp.right
+                predecessor = temp
+
+            # the minimum of the right subtree is the successor
+            if self.right is not None:
+                temp = self.right
+                while(temp.left):
+                    temp = temp.left
+                successor = temp
+
+            return
+
+        #if key is smaller than root, go to left subtree
+        if data < self.data:
+            print('Left')
+            self.left.findPredecessorAndSuccessor(data)
+        else:
+            print('Right')
+            self.right.findPredecessorAndSuccessor(data)
+
+    def insert(self, data):
+        ''' For inserting the data in the Tree '''
+        if self.data == data:
+            return False        # As BST cannot contain duplicate data
+
+        elif data < self.data:
+            ''' Data less than the root data is placed to the left of the root '''
+            if self.left:
+                return self.left.insert(data)
+            else:
+                self.left = Node(data)
+                return True
+
+        else:
+            ''' Data greater than the root data is placed to the right of the root '''
+            if self.right:
+                return self.right.insert(data)
+            else:
+                self.right = Node(data)
+                return True
+
+if __name__ == '__main__':
+    root = Node(50)
+    root.insert(30)
+    root.insert(20)
+    root.insert(40)
+    root.insert(70)
+    root.insert(60)
+    root.insert(80)
+
+    # following BST is created
+    #               50
+    #            /     \
+    #           30      70
+    #          /  \    /  \
+    #        20   40  60   80
+
+    root.findPredecessorAndSuccessor(70)
+    if  (predecessor is not None) and (successor is not None):
+        print('Predecessor:', predecessor.data, 'Successor:', successor.data)
+    else:
+        print('Predecessor:', predecessor, 'Successor:', successor)