数据结构学习笔记（五） 树的创建和遍历

创建（先序创建和根据先序和中序进行创建）和遍历（先序遍历、中序遍历、后序遍历、非递归堆栈遍历、层次遍历）：

package tree;

public class XianCreateTree {
    private static Node header;
    //非递归遍历的堆栈头指针
    private static Node first;
    //层次遍历的尾和头指针(队尾插入，对头出去)
    private static Node rear;
    private static Node front;
    private static int i;
    public static void main(String[] args) {　　　//这是先序创建
    //    char[] tree = new char[]{‘A‘,‘B‘,‘C‘,‘*‘,‘*‘,‘D‘,‘*‘,‘*‘,‘E‘,‘*‘,‘F‘,‘G‘,‘*‘,‘*‘,‘*‘};
    //    createTree(tree);

        char[] pre = new char[]{‘A‘,‘B‘,‘C‘,‘D‘,‘E‘,‘F‘,‘G‘};
        char[] mid = new char[]{‘C‘,‘B‘,‘D‘,‘A‘,‘E‘,‘G‘,‘F‘};
        header = new Node(pre[0]);
        preMid(pre,mid,header);
        System.out.print("先序遍历:");
        preTraverse(header);
        System.out.println();
        System.out.print("中序遍历:");
        midTraverse(header);
        System.out.println();
        System.out.print("后序遍历:");
        afterTraverse(header);
        System.out.println();//非递归遍历和层次遍历不能一起执行，因为都有next
//        System.out.print("非递归历:");
//        noRecursion(header);
//        System.out.println();
        System.out.print("层次遍历:");
        queue(header);
        System.out.println();
    }

    /*
     * 先序创建一棵二叉树
     */
    public static Node createTree(char[] tree){
        if(tree[i] == ‘*‘){
            return null;
        }
        Node node = new Node(tree[i]);
        if(header == null){
            header = node;
        }
        i++;
        node.left=createTree(tree);
        i++;
        node.right=createTree(tree);
        return node;
    }
    /**
     * 先 和 中创建一棵二叉树
     */
    public static Node preMid(char[] pre,char[] mid,Node node){
        int index  = getIndex(mid,node.data);
        //说明还有右子树
        int len = pre.length-1-index;

        char[] pre_left;
        char[] pre_right;
        char[] mid_left;
        char[] mid_right;
        if(index > 0){
            if(index == 1){
                node.left = new Node(mid[0]);
            }else{
                pre_left = new char[index];
                mid_left = new char[index];
                //arg0:源数组；arg1:源数组要复制的起始位置；arg2:目的数组；arg3:目的数组放置的起始位置；rg4:复制的长度。
                System.arraycopy(pre, 1, pre_left, 0, index);
                System.arraycopy(mid, 0, mid_left, 0, index);
                //找到根节点后的第一个节点
                //找到根节点后的第一个节点在中序的位置
                node.left = preMid(pre_left,mid_left,new Node(pre_left[0]));
            }
        }
        if(len > 0){
            if(len == 1){
                node.right = new Node(mid[index+1]);
            }else{
                pre_right = new char[len];
                mid_right = new char[len];
                System.arraycopy(pre, index+1, pre_right, 0, mid.length-index-1);
                System.arraycopy(mid, index+1, mid_right, 0, mid.length-index-1);
                node.right = preMid(pre_right,mid_right,new Node(pre_right[0]));
            }
        }
        return node;
    }
    public static int getIndex(char[] mid,char c){
        for (int i = 0; i < mid.length; i++) {
            if(mid[i] == c){
                return i;
            }
        }
        return -1;
    }
    /**
     * 先序遍历
     */
    public static Node preTraverse(Node node){
        if(node != null){
            System.out.print(node.data+" ");
            node.left = preTraverse(node.left);
            node.right = preTraverse(node.right);
        }
        return node;
    }

    /**
     * 中序遍历
     */
    public static Node midTraverse(Node node){
        if(node != null){
            node.left = midTraverse(node.left);
            System.out.print(node.data+" ");
            node.right = midTraverse(node.right);
        }
        return node;
    }

    /**
     * 后序遍历
     */
    public static Node afterTraverse(Node node){
        if(node != null){
            node.left = afterTraverse(node.left);
            node.right = afterTraverse(node.right);
            System.out.print(node.data+" ");
        }
        return node;
    }
    /*
     * 使用堆栈(堆栈里存放的是节点)非递归遍历(中序)
     */
    public static void noRecursion(Node node){
        first = new Node(‘o‘);
        //右子树
        while(node != null || first.next != null){
            //左子树
            while(node != null){
                //System.out.print(first.next.data +" ");先序
                node.next = first.next;
                first.next = node;
                node = node.left;
            }
            if(first.next != null){
                System.out.print(first.next.data +" ");
                node = first.next;
                first.next = first.next.next;
                node = node.right;
            }
        }
    }
    /**
     * 使用队列层次遍历
     */
    public static void queue(Node node){
        rear = front = node;
        while(front != null){
            if(front.left != null){
                rear.next = front.left;
                rear = rear.next;
            }
            if(front.right != null){
                rear.next = front.right;
                rear = rear.next;
            }
            System.out.print(front.data+" ");
            front = front.next;
        }
    }
}

树的结点类：

package tree;

public class Node {
    public char data;
    public Node left;
    public Node right;
    public Node next;
    public Node(char data) {
        super();
        this.data = data;
    }

}