SegmentTree basics come true two.

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

@@ -0,0 +1,8 @@
+/**
+ * @Auther: lss
+ * @Date: 2019/2/27 20:53
+ * @Description:
+ */
+public interface Merger<E> {
+ E merge(E a, E b);
+}

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

@@ -7,14 +7,37 @@ public class SegmentTree<E> {
 
  private E[] tree;
  private E[] data;
+ private Merger<E> merger;
 
- public SegmentTree(E[] arr) {
+ public SegmentTree(E[] arr, Merger<E> merger) {
+
+ this.merger = merger;
 
  data = (E[]) new Object[arr.length];
  for (int i = 0; i < arr.length; i++)
  data[i] = arr[i];
 
  tree = (E[]) new Object[4 * arr.length];
+ buildSegmentTree(0, 0, data.length);
+ }
+
+ // 在treeIndex的位置创建表示区间[l...r]的线段树
+ private void buildSegmentTree(int treeIndex, int l, int r) {
+
+ if (l == r) {
+ tree[treeIndex] = data[l];
+ return;
+ }
+
+ int leftTreeIndex = leftChild(treeIndex);
+ int rightTreeIndex = rightChild(treeIndex);
+ // l+r 可能会溢出 所以采用这种
+ int mid = l + (r - l) / 2;
+ buildSegmentTree(leftTreeIndex, l, mid);
+ buildSegmentTree(rightTreeIndex, mid + 1, r);
+
+ tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
+
  }
 
  public int getSize() {