3. 二叉树

1.二叉树节点结构

class Node<V>{
    V value;
    Node left;
    Node right;
}

用递归和非递归两种方式实现二叉树的先序、中序、后序遍历

如果直观的打印一颗二叉树

如何完成二叉树的宽度优先遍历（常见题目：求一颗二叉树的宽度）

# 二叉树先序遍历
public static void preOrderRecur(Node head){
    if(head == null){
        return;
    }
    System.out.print(head.value+" ");
    preOrderRecur(head.left);
    preOrderRecur(head.right);
}

# 二叉树中序遍历
public static void inOrderRecur(Node head){
    if(head == null){
        return;
    }
    preOrderRecur(head.left);
    System.out.print(head.value+" ");
    preOrderRecur(head.right);
}


# 二叉树后序遍历
public static void inOrderRecur(Node head){
    if(head == null){
        return;
    }
    preOrderRecur(head.left);
    preOrderRecur(head.right);
    System.out.print(head.value+" ");
}