二叉树删除节点，(查找二叉树最大值节点)

从根节点往下分别查找左子树和右子树的最大节点，再比较左子树，右子树，根节点的大小得到结果，在得到左子树和右子树最大节点的过程相似，因此可以采用递归的

//树节点结构
public class TreeNode {
    TreeNode left;
    TreeNode right;
    int val;
    TreeNode(int val){
        this.val = val;
    }
}
public class Solution {
    /**
     * @param root 传入根节点
     * @return 返回最大结果
     */
    public static TreeNode maxNode(TreeNode root){
        //当再无子节点，返回当前节点
        if (root == null) {
            return root;
        }

        TreeNode left = maxNode(root.left);//递归得到左子树最大值
        TreeNode right = maxNode(root.right);//递归得到右子树的最大值
        return max(root,max(left,right));//返回左节点，根节点,右节点的最大值

    }
    public static TreeNode max(TreeNode a,TreeNode b) {
        if (a == null) {
            return b;
        }
        if (b == null) {
            return a;
        }
        if (a.val > b.val) {
            return a;
        }
        return b;
    }
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(1);
        TreeNode t2 = new TreeNode(-5);
        TreeNode t3 = new TreeNode(3);
        TreeNode t4 = new TreeNode(1);
        TreeNode t5 = new TreeNode(2);
        TreeNode t6 = new TreeNode(-4);
        TreeNode t7 = new TreeNode(-5);
        t1.left = t2;t1.right = t5;
        t2.left = t3;t2.right = t4;
        t5.left = t6;t5.right = t7;
        System.out.println(Solution.maxNode(t1).val);
    }
}