segment tree

Segment Tree Modify.py

@@ -0,0 +1,47 @@
+"""
+For a Maximum Segment Tree, which each node has an extra value max to store the maximum value in this node's interval.
+
+Implement a modify function with three parameter root, index and value to change the node's value with [start, end] =
+[index, index] to the new given value. Make sure after this change, every node in segment tree still has the max
+attribute with the correct value.
+"""
+__author__ = 'Danyang'
+
+
+class SegmentTreeNode:
+    def __init__(self, start, end, max):
+        self.start, self.end, self.max = start, end, max
+        self.left, self.right = None, None
+
+
+class Solution:
+    def modify(self, root, index, value):
+        """
+        need bottom-up update the max
+        :type root: SegmentTreeNode
+        :param root: The root of segment tree and
+        :param index: change the node's value with [index, index] to the new given value
+        :param value: the new given value
+        :return: void
+        """
+        if root is None:
+            return
+        if index<root.start or index>root.end:
+            return
+        if root.start==index and root.end==index:
+            root.max = value
+            return
+
+        # bottom up 
+        self.modify(root.left, index, value)
+        self.modify(root.right, index, value)
+
+        m = value
+        if root.left:
+            m = max(m, root.left.max)
+        if root.right:
+            m = max(m, root.right.max)
+        root.max = m
+
+
+