统计和生成不同的二叉树

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import java.util.*;//统计和生成不同的二叉树public class generateBinaryTree{//二叉树节点的定义    public static class Node{public int value;public Node left;public Node right;public Node(int data){this.value=data;}}    //统计可能的二叉树的结构数    public static int numTrees(int n)    {    if(n<2){    return 1;    }    int[]num=new int[n+1];    num[0]=1;    //动态规划法    for(int i=1;i<n+1;i++)    {    for(int j=1;j<i+1;j++)    {    num[i]+=num[j-1]*num[i-j];    }        }        return num[n];    }    public static List<Node> generateTrees(int n) {return generate(1, n);}//********************************************************  //生成不同的二叉树public static List<Node> generate(int start, int end) {List<Node> res = new LinkedList<Node>();if (start > end) {res.add(null);}Node head = null;for (int i = start; i < end + 1; i++) {head = new Node(i);List<Node> lSubs = generate(start, i - 1);List<Node> rSubs = generate(i + 1, end);for (Node l : lSubs) {for (Node r : rSubs) {head.left = l;head.right = r;res.add(cloneTree(head));}}}return res;}public static Node cloneTree(Node head) {if (head == null) {return null;}Node res = new Node(head.value);//递归调用res.left = cloneTree(head.left);res.right = cloneTree(head.right);return res;}//**************************************************//直观打印二叉树public static void printTree(Node head) {System.out.println("Binary Tree:");printInOrder(head, 0, "H", 17);System.out.println();}public static void printInOrder(Node head, int height, String to, int len) {if (head == null) {return;}printInOrder(head.right, height + 1, "v", len);String val = to + head.value + to;int lenM = val.length();int lenL = (len - lenM) / 2;int lenR = len - lenM - lenL;val = getSpace(lenL) + val + getSpace(lenR);System.out.println(getSpace(height * len) + val);printInOrder(head.left, height + 1, "^", len);}public static String getSpace(int num) {String space = " ";StringBuffer buf = new StringBuffer("");for (int i = 0; i < num; i++) {buf.append(space);}return buf.toString();}//*************************************************public static void main(String[]args){int n = 4;System.out.println(numTrees(n));List<Node> res = generateTrees(n);for (Node node : res) {printTree(node);}}}
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