Java二叉树四种遍历算法

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构建二叉树

class Tree{    public Tree leftNode;//左节点    public Tree rightNode;//右节点    public int rootNode;//根节点    public Tree(int rootNode) {        this.rootNode = rootNode;    }    //向二叉树中插入节点    public void insertNode(Tree tree,int rootNode){        if (rootNode > tree.rootNode) {            if (tree.rightNode == null) {                tree.rightNode = new Tree(rootNode);            }else {                insertNode(tree.rightNode,rootNode);            }        }else {            if (tree.leftNode == null) {                tree.leftNode = new Tree(rootNode);            }else {                insertNode(tree.leftNode,rootNode);            }        }    }}

1、先根遍历
public static void preRoot(Tree tree){    if (tree != null) {        System.out.println(tree.rootNode);        preRoot(tree.leftNode);        preRoot(tree.rightNode);    }}

2、中根遍历public static void midRoot(Tree tree){    if (tree != null) {        midRoot(tree.leftNode);        System.out.println(tree.rootNode);        midRoot(tree.rightNode);    }}

3、//后根遍历public static void posRoot(Tree tree){    if (tree != null) {        posRoot(tree.leftNode);        posRoot(tree.rightNode);        System.out.println(tree.rootNode);    }}

4、//层次遍历public static void level(Tree tree){    if (tree != null) {        List<Tree> list = new ArrayList<Tree>();        list.add(tree);        while (!list.isEmpty()) {            Tree t = list.remove(0);            System.out.println(t.rootNode);            if (t.leftNode!=null) {                list.add(t.leftNode);            }            if (t.rightNode != null) {                list.add(t.rightNode);            }        }    }}

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