P125、面试题19：二叉树的镜像
题目：请完成一个函数，输入一个二叉树，该函数输出它的镜像
二叉树结点的定义如下：
struct BinaryTreeNode{
int m_nValue;
BinaryTreeNode* m_pLeft;
BinaryTreeNode* m_pRight;
}
求一棵树的镜像的过程：我们先前序比遍历这棵树的每个结点，如果遍历到的结点有子结点，就交换它的两个子结点。当交换完所有非叶子结点的左右子结点之后，就得到了树的镜像。
测试用例：
1）功能测试（普通二叉树，二叉树的所有结点都没有左子树或者右子树，只有一个结点的二叉树）；
2）特殊输入测试（二叉树的根节点为null指针）。
代码实现：
package com.yyq; /** * Created by Administrator on 2015/9/15. */ public class MirrorOfBinaryTree { public static BinaryTreeNode mirrorOfBinaryTree(BinaryTreeNode pNode) { if (pNode == null) return null; if (pNode.getM_pLeft() == null && pNode.getM_pRight() == null) return null; BinaryTreeNode pTemp = pNode.getM_pLeft(); pNode.setM_pLeft(pNode.getM_pRight()); pNode.setM_pRight(pTemp); if (pNode.getM_pLeft() != null) mirrorOfBinaryTree(pNode.getM_pLeft()); if (pNode.getM_pRight() != null) mirrorOfBinaryTree(pNode.getM_pRight()); return pNode; } //先序遍历 public static void preprintTree(BinaryTreeNode pRoot) { if (pRoot == null) return; System.out.print(pRoot.getM_nValue() + "\t"); preprintTree(pRoot.getM_pLeft()); preprintTree(pRoot.getM_pRight()); } //中序遍历 public static void midprintTree(BinaryTreeNode pRoot) { if (pRoot != null) { midprintTree(pRoot.getM_pLeft()); System.out.print(pRoot.getM_nValue() + "\t"); midprintTree(pRoot.getM_pRight()); } } public static void Test(String testName, BinaryTreeNode pRoot){ if (testName == null) return ; System.out.println("previous printing tree is:"); preprintTree(pRoot); System.out.println(); System.out.println("middle printing tree is:"); midprintTree(pRoot); System.out.println("\n====="+testName+": MirrorRecursively====="); BinaryTreeNode pNode1 = mirrorOfBinaryTree(pRoot); System.out.println("previous printing tree is:"); preprintTree(pNode1); System.out.println(); System.out.println("middle printing tree is:"); midprintTree(pNode1); System.out.println("\n====="+testName+": MirrorIteratively====="); BinaryTreeNode pNode2 = mirrorOfBinaryTree(pRoot); System.out.println("previous printing tree is:"); preprintTree(pNode2); System.out.println(); System.out.println("middle printing tree is:"); midprintTree(pNode2); System.out.println(); } // ====================测试代码==================== // 测试完全二叉树：除了叶子节点，其他节点都有两个子节点 // 8 // 6 10 // 5 7 9 11 public static void Test1() { System.out.println("\n=====Test1 starts:====="); BinaryTreeNode pNode8 = new BinaryTreeNode(8); BinaryTreeNode pNode6 = new BinaryTreeNode(6); BinaryTreeNode pNode10 = new BinaryTreeNode(10); BinaryTreeNode pNode5 = new BinaryTreeNode(5); BinaryTreeNode pNode7 = new BinaryTreeNode(7); BinaryTreeNode pNode9 = new BinaryTreeNode(9); BinaryTreeNode pNode11 = new BinaryTreeNode(11); pNode8.connectTreeNodes(pNode6, pNode10); pNode6.connectTreeNodes(pNode5, pNode7); pNode10.connectTreeNodes(pNode9, pNode11); Test("Test1",pNode8); pNode8 = null; } // 测试二叉树：出叶子结点之外，左右的结点都有且只有一个左子结点 // 8 // 7 // 6 // 5 // 4 public static void Test2() { System.out.println("\n=====Test2 starts:====="); BinaryTreeNode pNode8 = new BinaryTreeNode(8); BinaryTreeNode pNode7 = new BinaryTreeNode(7); BinaryTreeNode pNode6 = new BinaryTreeNode(6); BinaryTreeNode pNode5 = new BinaryTreeNode(5); BinaryTreeNode pNode4 = new BinaryTreeNode(4); pNode8.connectTreeNodes(pNode7, null); pNode7.connectTreeNodes(pNode6, null); pNode6.connectTreeNodes(pNode5, null); pNode5.connectTreeNodes(pNode4, null); Test("Test2",pNode8); pNode8 = null; } // 测试二叉树：出叶子结点之外，左右的结点都有且只有一个右子结点 // 8 // 7 // 6 // 5 // 4 public static void Test3() { System.out.println("\n=====Test3 starts:====="); BinaryTreeNode pNode8 = new BinaryTreeNode(8); BinaryTreeNode pNode7 = new BinaryTreeNode(7); BinaryTreeNode pNode6 = new BinaryTreeNode(6); BinaryTreeNode pNode5 = new BinaryTreeNode(5); BinaryTreeNode pNode4 = new BinaryTreeNode(4); pNode8.connectTreeNodes(null, pNode7); pNode7.connectTreeNodes(null, pNode6); pNode6.connectTreeNodes(null, pNode5); pNode5.connectTreeNodes(null, pNode4); Test("Test3",pNode8); pNode8 = null; } // 测试空二叉树：根结点为空指针 public static void Test4() { System.out.println("\n=====Test4 starts:====="); BinaryTreeNode pNode = null; Test("Test4",pNode); } // 测试只有一个结点的二叉树 public static void Test5() { System.out.println("\n=====Test5 starts:====="); BinaryTreeNode pNode8 = new BinaryTreeNode(8); Test("Test5",pNode8); pNode8 = null; } public static void main(String[] args) { Test1(); Test2(); Test3(); Test4(); Test5(); } }
输出结果：
=====Test1 starts:=====
previous printing tree is:
8 6 5 7 10 9 11
middle printing tree is:
5 6 7 8 9 10 11
=====Test1: MirrorRecursively=====
previous printing tree is:
8 10 11 9 6 7 5
middle printing tree is:
11 10 9 8 7 6 5
=====Test1: MirrorIteratively=====
previous printing tree is:
8 6 5 7 10 9 11
middle printing tree is:
5 6 7 8 9 10 11
=====Test2 starts:=====
previous printing tree is:
8 7 6 5 4
middle printing tree is:
4 5 6 7 8
=====Test2: MirrorRecursively=====
previous printing tree is:
8 7 6 5 4
middle printing tree is:
8 7 6 5 4
=====Test2: MirrorIteratively=====
previous printing tree is:
8 7 6 5 4
middle printing tree is:
4 5 6 7 8
=====Test3 starts:=====
previous printing tree is:
8 7 6 5 4
middle printing tree is:
8 7 6 5 4
=====Test3: MirrorRecursively=====
previous printing tree is:
8 7 6 5 4
middle printing tree is:
4 5 6 7 8
=====Test3: MirrorIteratively=====
previous printing tree is:
8 7 6 5 4
middle printing tree is:
8 7 6 5 4
=====Test4 starts:=====
previous printing tree is:
middle printing tree is:
=====Test4: MirrorRecursively=====
previous printing tree is:
middle printing tree is:
=====Test4: MirrorIteratively=====
previous printing tree is:
middle printing tree is:
=====Test5 starts:=====
previous printing tree is:
8
middle printing tree is:
8
=====Test5: MirrorRecursively=====
previous printing tree is:
middle printing tree is:
=====Test5: MirrorIteratively=====
previous printing tree is:
middle printing tree is:
