Java编写线段树代码

好的，我来帮你编写 Java 的线段树代码。

线段树是一种树形结构，其中每个节点都存储了一段区间的信息。它常常用于处理区间查询、修改等问题。

下面是一个线段树的简单实现，它可以处理区间求和问题：

class SegmentTree {
    private static class Node {
        int left;
        int right;
        int sum;
    }

    private Node[] tree;
    private int[] data;

    public SegmentTree(int[] data) {
        this.data = data;
        tree = new Node[data.length * 4];
        build(0, 0, data.length - 1);
    }

    private void build(int treeIndex, int left, int right) {
        if (left == right) {
            tree[treeIndex] = new Node();
            tree[treeIndex].left = left;
            tree[treeIndex].right = right;
            tree[treeIndex].sum = data[left];
            return;
        }
        int mid = left + (right - left) / 2;
        int leftTreeIndex = treeIndex * 2 + 1;
        int rightTreeIndex = treeIndex * 2 + 2;
        build(leftTreeIndex, left, mid);
        build(rightTreeIndex, mid + 1, right);
        tree[treeIndex] = new Node();
        tree[treeIndex].left = left;
        tree[treeIndex].right = right;
        tree[treeIndex].sum = tree[leftTreeIndex].sum + tree[rightTreeIndex].sum;
    }

    public void update(int index, int value) {
        update(0, index, value);
    }

    private void update(int treeIndex, int index, int value) {
        if (tree[treeIndex].left == tree[treeIndex].right) {
            tree[treeIndex].sum = value;
            return;
        }
        int mid = tree[treeIndex].left + (tree[treeIndex].right - tree[treeIndex].left) / 2;
        int leftTreeIndex = treeIndex * 2 + 1;
        int rightTreeIndex = treeIndex * 2 + 2;
        if (index <= mid) {
            update(leftTreeIndex, index, value);
        } else {
            update(rightTreeIndex, index, value);
        }
        tree[treeIndex].sum = tree[leftTreeIndex].sum + tree[rightTreeIndex].sum;
    }

    public int query(int left, int right) {
        return query(0, left, right);
    }

    private int query(int treeIndex, int left, int right) {
        if (left == tree[