SegmentTree query().

09-Segment-Tree/01-Segment-Tree-Basics/src/Main.java

@@ -6,13 +6,16 @@
 public class Main {
  public static void main(String[] args) {
 
- Integer[] nums = {-2, 0, 3, -5, 2 - 1};
+ Integer[] nums = {-2, 0, 3, -5, 2, - 1};
  SegmentTree<Integer> segmentTree = new SegmentTree<>(nums, new Merger<Integer>() {
  @Override
  public Integer merge(Integer a, Integer b) {
  return a + b;
  }
  });
- System.out.println(segmentTree);
+ // System.out.println(segmentTree);
+ System.out.println(segmentTree.query(0, 2));
+ System.out.println(segmentTree.query(2, 5));
+ System.out.println(segmentTree.query(0, 5));
  }
 }

09-Segment-Tree/01-Segment-Tree-Basics/src/SegmentTree.java

@@ -1,3 +1,5 @@
+import javax.xml.transform.Result;
+
 /**
  * @Auther: lss
  * @Date: 2019/2/26 20:53
@@ -60,6 +62,36 @@ private int rightChild(int index) {
  return 2 * index + 2;
  }
 
+ // 返回区间[queryL,queryR]的值
+ public E query(int queryL, int queryR) {
+
+ if (queryL < 0 || queryL >= data.length ||
+ queryR < 0 || queryR >= data.length || queryL > queryR)
+ throw new IllegalArgumentException("Index is illegal.");
+
+ return query(0, 0, data.length - 1, queryL, queryR);
+ }
+
+ // 在以treeId为根的线段树中[l...r]的范围里，搜索区间[queryL...queryR]的值
+ private E query(int treeIndex, int l, int r, int queryL, int queryR) {
+
+ if (l == queryL && r == queryR)
+ return tree[treeIndex];
+
+ int mid = l + (r - l) / 2;
+ int leftTreeIndex = leftChild(treeIndex);
+ int rightTreeIndex = rightChild(treeIndex);
+
+ if (queryL >= mid + 1)
+ return query(rightTreeIndex, mid + 1, r, queryL, queryR);
+ else if (queryR <= mid)
+ return query(leftTreeIndex, l, mid, queryL, queryR);
+
+ E leftResult = query(leftTreeIndex, l, mid, queryL, mid);
+ E rightResult = query(rightTreeIndex, mid + 1, r, mid + 1, queryR);
+ return merger.merge(leftResult, rightResult);
+ }
+
  @Override
  public String toString() {
  StringBuilder res = new StringBuilder();