Segment Tree Query I
For an integer array (index from 0 to n-1, where n is the size of this array), in the corresponding SegmentTree, each node stores an extra attribute max
to denote the maximum number in the interval of the array (index from start to end).
Design a query
method with three parameters root
, start
and end
, find the maximum number in the interval [start, end] by the given root of segment tree.
For array [1, 4, 2, 3]
, the corresponding Segment Tree is:
[0, 3, max=4]
/ \
[0,1,max=4] [2,3,max=3]
/ \ / \
[0,0,max=1] [1,1,max=4] [2,2,max=2], [3,3,max=3]
query(root, 1, 1), return 4
query(root, 1, 2), return 4
query(root, 2, 3), return 3
query(root, 0, 2), return 4
/**
* 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, start, end: The root of segment tree and
* an segment / interval
*@return: The maximum number in the interval [start, end]
*/
public int query(SegmentTreeNode root, int start, int end) {
if (root == null || root.start > end || root.end < start) return Integer.MIN_VALUE; if (root.start == start && root.end == end) return root.max; int mid = (root.start + root.end) / ;
if (start >= mid + ) {
return query(root.right, start, end);
} else if (end <= mid) {
return query(root.left, start, end);
} else {
return Math.max(query(root.left, start, mid), query(root.right, mid + , end));
} }
}
Segment Tree Query II
For an array, we can build a SegmentTree
for it, each node stores an extra attribute count
to denote the number of elements in the the array which value is between interval start and end. (The array may not fully filled by elements)
Design a query
method with three parameters root
,start
and end
, find the number of elements in the in array's interval [start, end] by the given root of value SegmentTree.
For array [0, 2, 3]
, the corresponding value Segment Tree is:
[0, 3, count=3]
/ \
[0,1,count=1] [2,3,count=2]
/ \ / \
[0,0,count=1] [1,1,count=0] [2,2,count=1], [3,3,count=1]
query(1, 1)
, return 0
query(1, 2)
, return 1
query(2, 3)
, return 2
query(0, 2)
, return 2
/**
* Definition of SegmentTreeNode:
* public class SegmentTreeNode {
* public int start, end, count;
* public SegmentTreeNode left, right;
* public SegmentTreeNode(int start, int end, int count) {
* this.start = start;
* this.end = end;
* this.count = count;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
*@param root, start, end: The root of segment tree and
* an segment / interval
*@return: The count number in the interval [start, end]
*/
public int query(SegmentTreeNode root, int start, int end) {
if (root == null || root.start > end || root.end < start) return ; // alert, special case
if (end > root.end) end = root.end;
if (start < root.start) start = root.start; if (root.start == start && root.end == end) return root.count; int mid = (root.start + root.end) / ; if (end <= mid) {
return query(root.left, start, end);
} else if (start >= mid + ) {
return query(root.right, start, end);
} else {
return query(root.right, mid + , end) + query(root.left, start, mid);
}
}
}