Merger接口：定义对区间如何操作
public interface Merger<E> { E merge(E a, E b); } SegmentTree：
public class SegmentTree<E> { private E[] tree; private E[] data; private Merger<E> merger; 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 - 1); } //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); int mid = l + (r - l) / 2;//mid = l + r buildSegmentTree(leftTreeIndex, l, mid); buildSegmentTree(rightTreeIndex, mid + 1, r); tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]); } //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treeIndex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); } public int getSize() { return data.length; } public E get(int index) { if(index < 0 || index >= data.length) { throw new IllegalArgumentException("Index is illegal."); } return data[index]; } //返回完全二叉树的数组表示中，一个索引所表示的元素的左孩子节点的索引 private int leftChild(int index) { return 2 * index + 1; } //返回完全二叉树的数组表示中，一个索引所表示的元素的右孩子节点的索引 private int rightChild(int index) { return 2 * index + 2; } //将index位置的值，更新为e public void set(int index, E e) { if(index < 0 || index >= data.length) { throw new IllegalArgumentException("Index is illegal."); } data[index] = e; set(0, 0, data.length - 1, index, e); } //在以treeIndex为根的线段树中更新index的值为e private void set(int treeIndex, int l, int r, int index, E e) { if(l == r) { tree[treeIndex] = e; return; } int mid = l + (r - l) / 2; int leftTreeIndex = leftChild(treeIndex); int rightTreeIndex = rightChild(treeIndex); if(index >= mid + 1) { set(rightTreeIndex, mid + 1, r, index, e); } else { set(leftTreeIndex, l, mid, index, e); } tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]); } @Override public String toString() { StringBuilder res = new StringBuilder(); res.append('['); for (int i = 0; i < tree.length; i++) { if (tree[i] != null) { res.append(tree[i]); } else { res.append("null"); } if (i != tree.length - 1) { res.append('-'); } else { res.append(']'); } } return res.toString(); } } 文章来源: https://blog.csdn.net/weixin_40617102/article/details/90301097