第21天 二叉树的深度遍历的递归实现

1. 二叉树是一个比较难搞的问题，但是通过递归实现就代码就比较简单(但是递归需要自己理解，可以通过画图来帮助自己理解)。
2. 二叉树的遍历比存储简单，下面的代码也会手动建立一个二叉树，并且创建求他结点个数和二叉树深度的方法，都用到了递归。
3. 二叉树里面包括前中后序的遍历，用到递归，方法里面内容相近，主要是输出语句的位置不同。

具体看代码：

package pt;

import java.util.Arrays;


public class BinaryCharTree {
	
	char value;

	
	BinaryCharTree leftChild;

	
	BinaryCharTree rightChild;

	
	public BinaryCharTree(char paraName) {
		value = paraName;
		leftChild = null;
		rightChild = null;
	}// of the constructor

	
	public static BinaryCharTree manualConstructorTree() {
		// Step 1. Construct a tree with only one node.
		BinaryCharTree resultTree = new BinaryCharTree('a');

		// Step 2. Construct all nodes. The first node is the root.
		// BinaryCharTreeNode tempTreeA=resultTree.root.
		BinaryCharTree tempTreeB = new BinaryCharTree('b');
		BinaryCharTree tempTreeC = new BinaryCharTree('c');
		BinaryCharTree tempTreeD = new BinaryCharTree('d');
		BinaryCharTree tempTreeE = new BinaryCharTree('e');
		BinaryCharTree tempTreeF = new BinaryCharTree('f');
		BinaryCharTree tempTreeG = new BinaryCharTree('g');

		// step 3.link all nodes.
		resultTree.leftChild = tempTreeB;
		resultTree.rightChild = tempTreeC;
		tempTreeB.rightChild = tempTreeD;
		tempTreeC.leftChild = tempTreeE;
		tempTreeD.leftChild = tempTreeF;
		tempTreeD.rightChild = tempTreeG;

		return resultTree;
	}

	
	public void preOrderVisit() {
		System.out.println("" + value + " ");

		if (leftChild != null) {
			leftChild.preOrderVisit();
		} // of if

		if (rightChild != null) {
			rightChild.preOrderVisit();
		} // of if
	}// of preOrderVisit

	
	public void inOrderVisit() {
		if (leftChild != null) {
			leftChild.inOrderVisit();
		} // of if

		System.out.println("" + value + " ");

		if (rightChild != null) {
			rightChild.postOrderVisit();
		} // of if
	}// of inOrderVisit

	
	public void postOrderVisit() {
		if (leftChild != null) {
			leftChild.postOrderVisit();
		} // of if

		if (rightChild != null) {
			rightChild.postOrderVisit();
		} // of if

		System.out.println("" + value + " ");
	}

	
	public int getDepth() {
		// It is a leaf.
		if ((leftChild == null) && (rightChild == null)) {
			return 1;
		} // of if

		// The depth of the left child.
		int tempLeftDepth = 0;
		if (leftChild != null) {
			tempLeftDepth = leftChild.getDepth();
		} // of if

		// The depth of the right child.
		int tempRightDepth = 0;
		if (rightChild != null) {
			tempRightDepth = rightChild.getDepth();
		} // of if

		// The depth should increment by 1.
		if (tempLeftDepth >= tempRightDepth) {
			return tempLeftDepth + 1;
		} else {
			return tempRightDepth + 1;
		} // of if
	}// of getDepth

	
	public int getNumNodes() {
		// It is a leaf.
		if ((leftChild == null) && (rightChild == null)) {
			return 1;
		} // of if

		// The number of nodes of the left child.
		int tempLeftNodes = 0;
		if (leftChild != null) {
			tempLeftNodes = leftChild.getNumNodes();
		} // of if

		// The number of nodes of the right child.
		int tempRightNodes = 0;
		if (rightChild != null) {
			tempRightNodes = rightChild.getNumNodes();
		} // of if

		// The total number of nodes.
		return tempLeftNodes + tempRightNodes + 1;
	}// of gerNumbders

	
	public static void main(String args[]) {
		BinaryCharTree tempTree = manualConstructorTree();
		System.out.println("rnPreorder visit:");
		tempTree.preOrderVisit();
		System.out.println("rnIn-order visit:");
		tempTree.inOrderVisit();
		System.out.println("rnPost-order visit:");
		tempTree.postOrderVisit();

		System.out.println("rnrnThe depth is: " + tempTree.getDepth());
		System.out.println("The number of nodes is: " + tempTree.getNumNodes());
	}// of main

}// of BinaryCharTree