剑指Offer-59

题目：

请实现一个函数来判断一棵二叉树是不是对称的。如果一棵二叉树和它的镜像一样，那么它是对称的。

实现

public class Solution59 {    public static boolean isSymmetrical2(BinaryTreeNode root) {        return isSymmetrical2(root, root);    }    private static boolean isSymmetrical2(BinaryTreeNode left, BinaryTreeNode right) {        if (left == null && right == null) {            return true;        }        if (left == null || right == null) {            return false;        }        if (left.value != right.value) {            return false;        }        return isSymmetrical2(left.left, right.right) && isSymmetrical2(left.right, right.left);    }    public static boolean isSymmetrical(BinaryTreeNode root){        if(root==null){            System.out.print("空树");        }        ArrayList node_list1 = new ArrayList();        //遍历树，将树各结点值存入list        traversal(node_list1,root);        //求树的镜像        mirrorTree(root);        ArrayList node_list2 = new ArrayList();        traversal(node_list2,root);        boolean result = compareList(node_list1,node_list2);        return result;    }    public static void traversal(ArrayList node_list,BinaryTreeNode root){        if(root==null){            return;        }        node_list.add(root.value);        traversal(node_list,root.left);        traversal(node_list,root.right);    }    public static void mirrorTree(BinaryTreeNode root){        if(root==null){            return;        }        BinaryTreeNode temp =root.left;        root.left = root.right;        root.right = temp;        mirrorTree(root.left);        mirrorTree(root.right);    }    public static boolean compareList(ArrayList list1,ArrayList list2){        if(list1.size()!=list2.size()){            return false;        }        int temp1=0;        int temp2=0;        for(int i=0;i<list1.size();i++){            temp1=(int)list1.get(i);            temp2=(int)list2.get(i);            if(temp1!=temp2){                return false;            }        }        return true;    }    public static void main(String[] args) {        test01();        test02();    }    private static void assemble(BinaryTreeNode node,                                 BinaryTreeNode left,                                 BinaryTreeNode right) {        node.left = left;        node.right = right;    }    //                            1    //                  2                   2    //             4         6          6          4    //          8     9   10   11   11     10   9     8    public static void test01() {        BinaryTreeNode n1 = new BinaryTreeNode(1);        BinaryTreeNode n2 = new BinaryTreeNode(2);        BinaryTreeNode n3 = new BinaryTreeNode(2);        BinaryTreeNode n4 = new BinaryTreeNode(4);        BinaryTreeNode n5 = new BinaryTreeNode(6);        BinaryTreeNode n6 = new BinaryTreeNode(6);        BinaryTreeNode n7 = new BinaryTreeNode(4);        BinaryTreeNode n8 = new BinaryTreeNode(8);        BinaryTreeNode n9 = new BinaryTreeNode(9);        BinaryTreeNode n10 = new BinaryTreeNode(10);        BinaryTreeNode n11 = new BinaryTreeNode(11);        BinaryTreeNode n12 = new BinaryTreeNode(11);        BinaryTreeNode n13 = new BinaryTreeNode(10);        BinaryTreeNode n14 = new BinaryTreeNode(9);        BinaryTreeNode n15 = new BinaryTreeNode(8);        assemble(n1, n2, n3);        assemble(n2, n4, n5);        assemble(n3, n6, n7);        assemble(n4, n8, n9);        assemble(n5, n10, n11);        assemble(n6, n12, n13);        assemble(n7, n14, n15);        assemble(n8, null, null);        assemble(n9, null, null);        assemble(n10, null, null);        assemble(n11, null, null);        assemble(n12, null, null);        assemble(n13, null, null);        assemble(n14, null, null);        assemble(n15, null, null);        System.out.println(isSymmetrical(n1));    }    //                            1    //                  2                   2    //             4         5          6          4    //          8     9   10   11   11     10   9     8    public static void test02() {        BinaryTreeNode n1 = new BinaryTreeNode(1);        BinaryTreeNode n2 = new BinaryTreeNode(2);        BinaryTreeNode n3 = new BinaryTreeNode(2);        BinaryTreeNode n4 = new BinaryTreeNode(4);        BinaryTreeNode n5 = new BinaryTreeNode(5);        BinaryTreeNode n6 = new BinaryTreeNode(6);        BinaryTreeNode n7 = new BinaryTreeNode(4);        BinaryTreeNode n8 = new BinaryTreeNode(8);        BinaryTreeNode n9 = new BinaryTreeNode(9);        BinaryTreeNode n10 = new BinaryTreeNode(10);        BinaryTreeNode n11 = new BinaryTreeNode(11);        BinaryTreeNode n12 = new BinaryTreeNode(11);        BinaryTreeNode n13 = new BinaryTreeNode(10);        BinaryTreeNode n14 = new BinaryTreeNode(9);        BinaryTreeNode n15 = new BinaryTreeNode(8);        assemble(n1, n2, n3);        assemble(n2, n4, n5);        assemble(n3, n6, n7);        assemble(n4, n8, n9);        assemble(n5, n10, n11);        assemble(n6, n12, n13);        assemble(n7, n14, n15);        assemble(n8, null, null);        assemble(n9, null, null);        assemble(n10, null, null);        assemble(n11, null, null);        assemble(n12, null, null);        assemble(n13, null, null);        assemble(n14, null, null);        assemble(n15, null, null);        System.out.println(isSymmetrical(n1));    }}