SegmentTree.java

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);
	}
	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;
		buildSegmentTree(leftTreeIndex,l,mid);
		buildSegmentTree(rightTreeIndex,mid+1,r);
		tree[treeIndex]=merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
	}
	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];
	}
	private int leftChild(int index) {
		return 2*index+1;
	}
	public int rightChild(int index) {
		return 2*index+2;
	}
	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);
	}
	
	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();
		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();
	}
	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);
	}
	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]);
	}
}