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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.
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]
1 /** 2 * Definition of SegmentTreeNode: 3 * public class SegmentTreeNode { 4 * public int start, end, max; 5 * public SegmentTreeNode left, right; 6 * public SegmentTreeNode(int start, int end, int max) { 7 * this.start = start; 8 * this.end = end; 9 * this.max = max 10 * this.left = this.right = null; 11 * } 12 * } 13 */ 14 public class Solution { 15 /** 16 *@param root, index, value: The root of segment tree and 17 *@ change the node‘s value with [index, index] to the new given value 18 *@return: void 19 */ 20 public void modify(SegmentTreeNode root, int index, int value) { 21 changeAndUpdate(root, index, value); 22 } 23 24 private void changeAndUpdate(SegmentTreeNode root, int index, int value) { 25 if (root.start == index && root.end == index) { 26 root.max = value; 27 return; 28 } 29 30 int mid = (root.start + root.end) / 2; 31 if (mid >= index) { 32 change(root.left, index, value); 33 } else { 34 change(root.right, index, value); 35 } 36 root.max = Math.max(root.left.max, root.right.max); 37 } 38 }
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原文地址：http://www.cnblogs.com/beiyeqingteng/p/5655096.html
