import java.util.*;
class BinaryTree {
static class TreeNode {
public char val;
public TreeNode left;//左孩子的引用
public TreeNode right;//右孩子的引用
public TreeNode(char val) {
this.val = val;
}
}
//创建一棵二叉树,返回这棵树的根节点
public TreeNode createTree() {
TreeNode A = new TreeNode('A');
TreeNode B = new TreeNode('B');
TreeNode C = new TreeNode('C');
TreeNode D = new TreeNode('D');
TreeNode E = new TreeNode('E');
TreeNode F = new TreeNode('F');
TreeNode G = new TreeNode('G');
TreeNode H = new TreeNode('H');
A.left = B;
A.right = C;
B.left = D;
B.right = E;
C.left = F;
C.right = G;
E.right = H;
return A;
}
//前序遍历1
public void preOrder(TreeNode root) {
if (root == null) {
return;
}
System.out.print(root.val + " ");
preOrder(root.left);
preOrder(root.right);
}
//前序遍历2
public List<Character> preorderTraversal(TreeNode root) {
//如果<>里是TreeNode，则下面是list.add(root)
List<Character> list = new ArrayList<>();//向上转型，每递归一次就创建一个List<Character>类型的变量list
if (root == null) {
return list;
}
list.add(root.val);
List<Character> leftTree = preorderTraversal(root.left);
list.addAll(leftTree);
List<Character> rightTree = preorderTraversal(root.right);
list.addAll(rightTree);
return list;
}
//中序遍历1
void inOrder(TreeNode root) {
if (root == null) {
return;
}
inOrder(root.left);
System.out.print(root.val + " ");
inOrder(root.right);
}
//中序遍历2
public List<Character> inorderTraversal(TreeNode root) {
List<Character> list = new ArrayList<>();
if (root == null) {
return list;
}
List<Character> leftTree = inorderTraversal(root.left);
list.addAll(leftTree);
list.add(root.val);
List<Character> rightTree = inorderTraversal(root.right);
list.addAll(rightTree);
return list;
}
//后序遍历1
void postOrder(TreeNode root) {
if (root == null) {
return;
}
postOrder(root.left);
postOrder(root.right);
System.out.print(root.val + " ");
}
//后序遍历2
public List<Character> postorderTraversal(TreeNode root) {
List<Character> list = new ArrayList<>();
if (root == null) {
return list;
}
List<Character> leftTree = postorderTraversal(root.left);
list.addAll(leftTree);
List<Character> rightTree = postorderTraversal(root.right);
list.addAll(rightTree);
list.add(root.val);
return list;
}
public static int nodeSize;
//获取树中节点的个数：遍历思路
void size(TreeNode root) {
//返回值为void
if (root == null) {
return;
}
nodeSize++;
size(root.left);
size(root.right);
}
//获取树中节点的个数：子问题思路
int size2(TreeNode root) {
//返回值为int
if (root == null) {
return 0;
}
return size2(root.left) + size2(root.right) + 1;
}
public static int leafSize = 0;
//获取叶子节点的个数：遍历思路
void getLeafNodeCount1(TreeNode root) {
if (root == null) {
return;
}
if (root.left == null && root.right == null) {
leafSize++;
}
getLeafNodeCount1(root.left);
getLeafNodeCount1(root.right);
}
//获取叶子节点的个数：子问题思路
int getLeafNodeCount2(TreeNode root) {
if (root == null) {
return 0;
}
if (root.left == null && root.right == null) {
return 1;
}
return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
}
//获取第K层节点的个数
int getKLevelNodeCount(TreeNode root, int k) {
//root这棵树第k层节点数量=root.left这棵树第k-1层节点数量+root.right这棵树第k-1层节点数量
if (root == null) {
return 0;
}
if (k == 1) {
//root不为null且k为1时，相当于属于第k层的一个节点数
return 1;
}
return getKLevelNodeCount(root.left, k - 1) + getKLevelNodeCount(root.right, k - 1);
}
//获取二叉树的高度，时间复杂度：O(N)
int getHeight(TreeNode root) {
if (root == null) {
return 0;
}
int leftTreeHeight = getHeight(root.left);
int rightTreeHeight = getHeight(root.right);
return leftTreeHeight > rightTreeHeight ? leftTreeHeight + 1 : rightTreeHeight + 1;
}
// 检测值为value的元素是否存在
boolean find(TreeNode root, char key) {
if(root == null) {
return false;
}
if(root.val == key) {
return true;
}
boolean leftVal = find(root.left, key);
if(leftVal == true) {
return true;
}
boolean rightVal = find(root.right, key);
if(rightVal == true) {
return true;
}
return false;
}
//层序遍历
//法一：返回值为void
void levelOrder1(TreeNode root) {
if(root == null) {
return;
}
Queue<TreeNode> queue = new LinkedList<>();//链表实现队列
queue.offer(root);
while(!queue.isEmpty()) {
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);
}
}
}
//法二：返回值为List<List<TreeNode>>
List<List<TreeNode>> levelOrder2(TreeNode root) {
List<List<TreeNode>> ret = new ArrayList<>();//顺序表里面的每个元素又是一个顺序表
if(root == null) {
return ret;
}
Queue<TreeNode> queue = new LinkedList<>();//链表实现队列
queue.offer(root);
while(!queue.isEmpty()) {
int size = queue.size();//计算某一层一共有多少个节点
List<TreeNode> tmp = new ArrayList<>();
while(size != 0) {
TreeNode cur = queue.poll();
tmp.add(cur);
size--;
if (cur.left != null) {
queue.offer(cur.left);
}
if (cur.right != null) {
queue.offer(cur.right);
}
}
ret.add(tmp);
}
return ret;
}
// 判断一棵树是不是完全二叉树
boolean isCompleteTree(TreeNode root) {
if (root == null) {
return true;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode cur = queue.poll();
if(cur != null) {
queue.offer(cur.left);
queue.offer(cur.right);
}else {
//此时cur为null，即队列弹出第一个null
break;
}
}
while (!queue.isEmpty()) {
//队列弹出第一个null后，若后面还能弹出非null的节点，则不是完全二叉树
TreeNode cur = queue.poll();
if (cur != null) {
return false;
}
}
return true;
}
}
模拟实现二叉树的基本操作
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转载自blog.csdn.net/zhanlongsiqu/article/details/131771939
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