从后序遍历还原二叉树

Posted 2020-12-23 redo19990701

从后序遍历还原二叉树

/**
 * @Date 2020/5/31
 * @Author Redo
 * @Description 从后序遍历输出中重建二叉树
 **/
public class RecoverTreeFromPostOrderOutput {
    static class Node{
        int data;
        Node l;
        Node r;
        public Node(){};

        public Node(int data){
            this.data=data;
            l=null;
            r=null;
        }

        public static void PostOrderPrint(Node node){
            if(node==null)
                return;
            PostOrderPrint(node.l);
            PostOrderPrint(node.r);
            System.out.print(node.data+" ");
        }
    }
    private static Node recover(int[] arr,int start,int end){
        //该子树为空
        if(start>end)
            return null;
        //末尾数字总是父节点
        int head= arr[end];
        Node node=new Node(head);
        //左子树总是小于父节点,右子树总是大于父节点
        int i=start;
        for(;i<end;i++){
            if(arr[i]>head)
                break;
        }
        node.l= recover(arr,start,i-1);
        node.r= recover(arr,i,end-1);
        return node;
    }
    public static Node recover(int[] arr){
        return recover(arr,0,arr.length-1);
    }

    public static void main(String[] args) {
        int[] arr={2,4,3,6,8,7,5};
        Node node=recover(arr);
        Node.PostOrderPrint(node);
    }
}