二叉树系列—恢复二叉树

##先序与中序：

public class ReBuildBinaryTree{
	public static void main(String[] args) {	
		int[] pre={1,2,4,7,3,5,6,8};
		int[] mid={4,7,2,1,5,3,8,6};
		
		Node root=rebuild(pre, mid);
		show(root);
		
	}
	//思想：利用先序遍历对中序遍历分割
	public static Node rebuild(int[] pre,int[] mid){
		if(pre==null||mid==null||pre.length!=mid.length){
			return null;
		}
		HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();
		for(int i=0;i<mid.length;i++){
			map.put(mid[i], i);
		}
		return build(pre,0,pre.length-1,mid,0,mid.length-1,map);
	}
	private static Node build(int[] pre, int ps, int pe, int[] mid, int ms, int me, HashMap<Integer, Integer> map) {
		if(ps>pe){
			return null;
		}
		Node head=new Node();
		head.data=pre[ps];
		int index=map.get(pre[ps]);
		head.left=build(pre, ps+1, index+ps-ms, mid, ms, index-1, map);
		head.right=build(pre,index+ps-ms+1, pe, mid, index+1, me, map);
		//中序与后序恢复二叉树
		//head.left=build(mid,ms,index-1,pos,ps,ps+index-ms-1,map);
		//head.right=build(mid,index+1,me,pos,ps+index-ms,pe-1,map);
		return head;
	}
	private static class Node{
		int data;
		Node left,right;
	}
	public static void show(Node head){
		if(head!=null){
			Queue<Node> queue=new LinkedList<Node>();
			queue.offer(head);
			while(!queue.isEmpty()){
				head=queue.poll();
				System.out.print(head.data+" ");
				if(head.left!=null){
					queue.offer(head.left);
				}
				if(head.right!=null){
					queue.offer(head.right);
				}
			}
			
		}
	}
}