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 parameterroot, 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.
Example
For segment tree:
[1, 4, max=3]
/ \
[1, 2, max=2] [3, 4, max=3]
/ \ / \
[1, 1, max=2], [2, 2, max=1], [3, 3, max=0], [4, 4, max=3]
if call modify(root, 2, 4), we can get:
[1, 4, max=4]
/ \
[1, 2, max=4] [3, 4, max=3]
/ \ / \
[1, 1, max=2], [2, 2, max=4], [3, 3, max=0], [4, 4, max=3]
or call modify(root, 4, 0), we can get:
[1, 4, max=2]
/ \
[1, 2, max=2] [3, 4, max=0]
/ \ / \
[1, 1, max=2], [2, 2, max=1], [3, 3, max=0], [4, 4, max=0]
/**
* Definition of SegmentTreeNode:
* public class SegmentTreeNode {
* public int start, end, max;
* public SegmentTreeNode left, right;
* public SegmentTreeNode(int start, int end, int max) {
* this.start = start;
* this.end = end;
* this.max = max
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
*@param root, index, value: The root of segment tree and
*@ change the node's value with [index, index] to the new given value
*@return: void
*/
public void modify(SegmentTreeNode root, int index, int value) {
changeAndUpdate(root, index, value);
} private void changeAndUpdate(SegmentTreeNode root, int index, int value) {
if (root.start == index && root.end == index) {
root.max = value;
return;
} int mid = (root.start + root.end) / ;
if (mid >= index) {
change(root.left, index, value);
} else {
change(root.right, index, value);
}
root.max = Math.max(root.left.max, root.right.max);
}
}