前、中、后序遍历二叉树

二叉树的遍历：前序遍历，中序遍历，后序遍历，层次遍历

如何进行前序遍历：

1、  先遍历树根

2、  然后前序遍历左子树

3、  再前序遍历右子树

如何进行中序遍历：

1、  先中序遍历左子树

2、  然后遍历树根

3、  再中序遍历右子树

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如何进行后序遍历：

1、  先后序遍历左子树

2、  然后后序遍历右子树

3、  再遍历树根

前序：ABDEGCF

中序：DBGEACF

后序：DGEBFCA

代码示例：

package com.sise.recursion;
/*
 * 遍历
 */
public class TreeTraversal {
	/*
	 * 前序遍历
	 */
	public void preOrder(TreeNode root) {
		if(root==null){
			return;
		}
		System.out.print(root.getValue());
		preOrder(root.getLeft());
		preOrder(root.getRighe());
	}
	
	/*
	 * 中序遍历
	 */
	public void inOrder(TreeNode root) {
		if(root==null){
			return;
		}
		inOrder(root.getLeft());
		System.out.print(root.getValue());
		inOrder(root.getRighe());
	}
	
	/*
	 * 后序遍历
	 */
	public void postOrder(TreeNode root) {
		if(root==null){
			return;
		}
		postOrder(root.getLeft());
		postOrder(root.getRighe());
		System.out.print(root.getValue());
	}
	
	
	public static void main(String[] args) {
		TreeCreator creator=new TreeCreator();
		TreeTraversal traversal=new TreeTraversal();
		
		TreeNode sampleTree=creator.createSampleTree();
		System.out.print("前序：");
		traversal.preOrder(sampleTree);
		System.out.println();
		System.out.print("中序：");
		traversal.inOrder(sampleTree);
		System.out.println();
		System.out.print("后序：");
		traversal.postOrder(sampleTree);
		System.out.println();
	}
}

package com.sise.recursion;

/*
 * 建树
 */
public class TreeCreator {
	public TreeNode createSampleTree() {
	TreeNode root=new TreeNode('A');
	root.setLeft(new TreeNode('B'));
	root.getLeft().setLeft(new TreeNode('D'));
	root.getLeft().setRighe(new TreeNode('E'));
	root.getLeft().getRighe().setLeft(new TreeNode('G'));
	root.setRighe(new TreeNode('C'));
	root.getRighe().setRighe(new TreeNode('F'));
	return root;
	}
}

package com.sise.recursion;

public class TreeNode {
	private final char value;
	private TreeNode left;
	private TreeNode righe;
	
	public TreeNode (char value) {
		this.value=value;
		this.left=null;
		this.righe=null;
	}

	public TreeNode getLeft() {
		return left;
	}

	public void setLeft(TreeNode left) {
		this.left = left;
	}

	public TreeNode getRighe() {
		return righe;
	}

	public void setRighe(TreeNode righe) {
		this.righe = righe;
	}

	public char getValue() {
		return value;
	}
	
	
}

运行结果：