Java實現(xiàn)二叉樹的示例代碼(遞歸&迭代)

更新時間：2022年03月17日 15:24:42 作者：愛干飯的猿

二叉樹（Binary?tree）是樹形結(jié)構(gòu)的一個重要類型。本文將利用Java語言實現(xiàn)二叉樹，文中的示例代碼講解詳細(xì)，需要的同學(xué)可以參考一下

//基礎(chǔ)二叉樹實現(xiàn)
//使用左右孩子表示法
 
import java.util.*;
import java.util.Deque;
 
public class myBinTree {
    private static class TreeNode{
        char val;
        TreeNode left;
        TreeNode right;
 
        public TreeNode(char val) {
            this.val = val;
        }
    }
 
    public static TreeNode build(){
        TreeNode nodeA=new TreeNode('A');
        TreeNode nodeB=new TreeNode('B');
        TreeNode nodeC=new TreeNode('C');
        TreeNode nodeD=new TreeNode('D');
        TreeNode nodeE=new TreeNode('E');
        TreeNode nodeF=new TreeNode('F');
        TreeNode nodeG=new TreeNode('G');
        TreeNode nodeH=new TreeNode('H');
        nodeA.left=nodeB;
        nodeA.right=nodeC;
        nodeB.left=nodeD;
        nodeB.right=nodeE;
        nodeE.right=nodeH;
        nodeC.left=nodeF;
        nodeC.right=nodeG;
        return nodeA;
    }
 
    //方法1(遞歸)
    //先序遍歷: 根左右
    public static void preOrder(TreeNode root){
        if(root==null){
            return;
        }
        System.out.print(root.val+" ");
        preOrder(root.left);
        preOrder(root.right);
    }
 
    //方法1(遞歸)
    //中序遍歷
    public static void inOrder(TreeNode root){
        if(root==null){
            return;
        }
        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
    }
 
    //方法1(遞歸)
    //后序遍歷
    public static void postOrder(TreeNode root){
        if(root==null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val+" ");
    }
 
    //方法2(迭代)
    //先序遍歷 (迭代)
    public static void preOrderNonRecursion(TreeNode root){
        if(root==null){
            return ;
        }
        Deque<TreeNode> stack=new LinkedList<>();
        stack.push(root);
        while (!stack.isEmpty()){
            TreeNode cur=stack.pop();
            System.out.print(cur.val+" ");
            if(cur.right!=null){
                stack.push(cur.right);
            }
            if(cur.left!=null){
                stack.push(cur.left);
            }
        }
    }
 
    //方法2(迭代)
    //中序遍歷 (迭代)
    public static void inorderTraversalNonRecursion(TreeNode root) {
        if(root==null){
            return ;
        }
 
        Deque<TreeNode> stack=new LinkedList<>();
        // 當(dāng)前走到的節(jié)點(diǎn)
        TreeNode cur=root;
        while (!stack.isEmpty() || cur!=null){
            // 不管三七二十一，先一路向左走到根兒~
            while (cur!=null){
                stack.push(cur);
                cur=cur.left;
            }
            // 此時cur為空，說明走到了null，此時棧頂就存放了左樹為空的節(jié)點(diǎn)
            cur=stack.pop();
            System.out.print(cur.val+" ");
            // 繼續(xù)訪問右子樹
            cur=cur.right;
        }
    }
 
    //方法2(迭代)
    //后序遍歷 (迭代)
    public static void postOrderNonRecursion(TreeNode root){
        if(root==null){
            return;
        }
        Deque<TreeNode> stack=new LinkedList<>();
        TreeNode cur=root;
        TreeNode prev=null;
 
        while (!stack.isEmpty() || cur!=null){
            while (cur!=null){
                stack.push(cur);
                cur=cur.left;
            }
 
            cur=stack.pop();
            if(cur.right==null || prev==cur.right){
                System.out.print(cur.val+" ");
                prev=cur;
                cur=null;
            }else {
                stack.push(cur);
                cur=cur.right;
            }
        }
    }
 
    //方法1(遞歸)
    //傳入一顆二叉樹的根節(jié)點(diǎn)，就能統(tǒng)計出當(dāng)前二叉樹中一共有多少個節(jié)點(diǎn)，返回節(jié)點(diǎn)數(shù)
    //此時的訪問就不再是輸出節(jié)點(diǎn)值，而是計數(shù)器 + 1操作
    public static int getNodes(TreeNode root){
        if(root==null){
            return 0;
        }
        return 1+getNodes(root.left)+getNodes(root.right);
    }
 
    //方法2(迭代)
    //使用層序遍歷來統(tǒng)計當(dāng)前樹中的節(jié)點(diǎn)個數(shù)
    public static int getNodesNoRecursion(TreeNode root){
        if(root==null){
            return 0;
        }
        int size=0;
        Deque<TreeNode> queue=new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            TreeNode cur = queue.poll();
            size++;
            if (cur.left != null) {
                queue.offer(cur.left);
            }
            if (cur.right != null) {
                queue.offer(cur.right);
            }
        }
        return size;
    }
 
    //方法1(遞歸)
    //傳入一顆二叉樹的根節(jié)點(diǎn)，就能統(tǒng)計出當(dāng)前二叉樹的葉子結(jié)點(diǎn)個數(shù)
    public static int getLeafNodes(TreeNode root){
        if(root==null){
            return 0;
        }
        if(root.left==null && root.right==null){
            return 1;
        }
        return getLeafNodes(root.left)+getLeafNodes(root.right);
    }
 
    //方法2(迭代)
    //使用層序遍歷來統(tǒng)計葉子結(jié)點(diǎn)的個數(shù)
    public static int getLeafNodesNoRecursion(TreeNode root){
        if(root==null){
            return 0;
        }
        int size=0;
        Deque<TreeNode> queue=new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()){
            TreeNode cur=queue.poll();
            if(cur.left==null && cur.right==null){
                size++;
            }
            if(cur.left!=null){
                queue.offer(cur.left);
            }
            if(cur.right!=null){
                queue.offer(cur.right);
            }
        }
        return size;
    }
 
    //層序遍歷
    public static void levelOrder(TreeNode root) {
        if(root==null){
            return ;
        }
 
        // 借助隊列來實現(xiàn)遍歷過程
        Deque<TreeNode> queue =new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()){
            int size=queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode cur=queue.poll();
                System.out.print(cur.val+" ");
                if(cur.left!=null){
                    queue.offer(cur.left);
                }
                if(cur.right!=null){
                    queue.offer(cur.right);
                }
            }
        }
    }
 
    //傳入一個以root為根節(jié)點(diǎn)的二叉樹，就能求出該樹的高度
    public static int height(TreeNode root){
        if(root==null){
            return 0;
        }
        return 1+ Math.max(height(root.left),height(root.right));
    }
 
    //求出以root為根節(jié)點(diǎn)的二叉樹第k層的節(jié)點(diǎn)個數(shù)
    public static int getKLevelNodes(TreeNode root,int k){
        if(root==null || k<=0){
            return 0;
        }
        if(k==1){
            return 1;
        }
        return getKLevelNodes(root.left,k-1)+getKLevelNodes(root.right,k-1);
    }
 
    //判斷當(dāng)前以root為根節(jié)點(diǎn)的二叉樹中是否包含指定元素val，
    //若存在返回true，不存在返回false
    public static boolean contains(TreeNode root,char value){
        if(root==null){
            return false;
        }
        if(root.val==value){
            return true;
        }
        return contains(root.left,value) || contains(root.right,value);
    }
 
 
    public static void main(String[] args) {
        TreeNode root=build();
 
        System.out.println("方法1(遞歸)：前序遍歷的結(jié)果為:");
        preOrder(root);
        System.out.println();
        System.out.println("方法2(迭代)：前序遍歷的結(jié)果為:");
        preOrderNonRecursion(root);
        System.out.println();
 
        System.out.println("方法1(遞歸)：中序遍歷的結(jié)果為:");
        inOrder(root);
        System.out.println();
        System.out.println("方法2(迭代)：中序遍歷的結(jié)果為:");
        inorderTraversalNonRecursion(root);
        System.out.println();
 
        System.out.println("方法1(遞歸)：后序遍歷的結(jié)果為:");
        postOrder(root);
        System.out.println();
        System.out.println("方法2(迭代)：后序遍歷的結(jié)果為:");
        postOrderNonRecursion(root);
        System.out.println();
        System.out.println();
 
        System.out.println("層序遍歷的結(jié)果為:");
        levelOrder(root);
        System.out.println();
        System.out.println();
 
        System.out.println("方法1(遞歸)：當(dāng)前二叉樹一共有:"+getNodes(root)+"個節(jié)點(diǎn)數(shù)");
        System.out.println("方法2(迭代)：當(dāng)前二叉樹一共有:"+getNodesNoRecursion(root)+"個節(jié)點(diǎn)數(shù)");
        System.out.println("方法1(遞歸)：當(dāng)前二叉樹一共有:"+getLeafNodes(root)+"個葉子節(jié)點(diǎn)數(shù)");
        System.out.println("方法2(迭代)：當(dāng)前二叉樹一共有:"+getLeafNodesNoRecursion(root)+"個葉子節(jié)點(diǎn)數(shù)");
        System.out.println(contains(root,'E'));
        System.out.println(contains(root,'P'));
        System.out.println("當(dāng)前二叉樹的高度為:"+height(root));
        System.out.println("當(dāng)前二叉樹第3層的節(jié)點(diǎn)個數(shù)為:"+getKLevelNodes(root,3));
    }
}

如上main引用結(jié)果如下：