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BinaryTree.java 20.52 KB
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杨昕上 提交于 2022-01-24 15:53 +08:00 . 二叉树代码完结
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import java.util.*;
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;
}
}
public class BinaryTree {
public static int i = 0;
public TreeNode createTree(String str) {
TreeNode root = null;
if (str.charAt(i) != '#') {
root = new TreeNode(str.charAt(i));
i++;
root.left = createTree(str);
root.right = createTree(str);
} else {
i++;
}
return root;
}
public TreeNode createTree1() {
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;
}
/*public static int i = 0 ;
public static TreeNode createTree(String str) {
TreeNode root = null;
if(str.charAt(i) != '#') {
root = new TreeNode(str.charAt(i));
i++;
root.left = createTree(str);
root.right = createTree(str);
}else {
//遇到# 就是空树
i++;
}
return root;
}
public static void inorder(TreeNode root) {
if(root == null) {
return;
}
inorder(root.left);
System.out.print(root.val+" ");
inorder(root.right);
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
// 注意 hasNext 和 hasNextLine 的区别
while (in.hasNextLine()) { // 注意 while 处理多个 case
String str = in.nextLine();
TreeNode root = createTree(str);
inorder(root);
}
}*/
// 前序遍历
void preOrder(TreeNode root) {
if (root == null) {
return;
}
System.out.print(root.val + " ");
preOrder(root.left);
preOrder(root.right);
}
//shift+f6->回车才会生效
public List<Character> preorderTraversal(TreeNode root) {
List<Character> retlist = new ArrayList<>();
if (root == null) {
return retlist;
}
retlist.add(root.val);
List<Character> leftTree = preorderTraversal(root.left);
retlist.addAll(leftTree);
List<Character> rightTree = preorderTraversal(root.right);
retlist.addAll(rightTree);
return retlist;
}
// 中序遍历
void inOrder(TreeNode root) {
if (root == null) {
return;
}
inOrder(root.left);
System.out.print(root.val + " ");
inOrder(root.right);
}
/*public List<Integer> inorderTraversal(TreeNode root) {
List<Integer> retlist = new ArrayList<>();
if(root == null) {
return retlist;
}
List<Integer> leftTree = inorderTraversal(root.left);
retlist.addAll(leftTree);
retlist.add(root.val);
List<Integer> rightTree =inorderTraversal(root.right);
retlist.addAll(rightTree);
return retlist;
}*/
// 后序遍历
void postOrder(TreeNode root) {
if (root == null) {
return;
}
postOrder(root.left);
postOrder(root.right);
System.out.print(root.val + " ");
}
//层序遍历
public void levelOrder(TreeNode root) {
Queue<TreeNode> queue = new LinkedList<>();
if (root == null) {
return;
}
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);
}
}
}
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> ret = new ArrayList<>();
if (root == null) {
return ret;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
int size = queue.size();
List<Integer> list = new ArrayList<>();
while (size != 0) {
TreeNode cur = queue.poll();
list.add(cur.val);
if (cur.left != null) {
queue.offer(cur.left);
}
if (cur.right != null) {
queue.offer(cur.right);
}
size--;
}
ret.add(list);
}
return ret;
}
/*public List<Integer> postorderTraversal(TreeNode root) {
List<Integer> retlist = new ArrayList<>();
if(root == null) {
return retlist;
}
List<Integer> leftTree = postorderTraversal
(root.left);
retlist.addAll(leftTree);
List<Integer> rightTree =postorderTraversal(root.right);
retlist.addAll(rightTree);
retlist.add(root.val);
return retlist;
}*/
/**
* 获取树中节点的个数
*/
int count = 0;
int size(TreeNode root) {
if (root == null) {
return 0;
}
count++;
size(root.left);
size(root.right);
return count;
}
// 子问题思路
int size1(TreeNode root) {
if (root == null) {
return 0;
}
return 1 + size1(root.left) + size1(root.right);
}
// 获取叶子节点的个数
int countLeaf = 0;
int getLeafNodeCount(TreeNode root) {
if (root == null) {
return 0;
}
if (root.left == null && root.right == null) {
countLeaf++;
}
getLeafNodeCount(root.left);
getLeafNodeCount(root.right);
return countLeaf;
}
//子问题思路
int getLeafNodeCount1(TreeNode root) {
if (root == null) {
return 0;
}
if (root.left == null && root.right == null) {
return 1;
}
return getLeafNodeCount1(root.left) + getLeafNodeCount1(root.right);
}
// 获取第K层节点的个数
int getKLevelNodeCount(TreeNode root, int k) {
if (root == null || k < 1) {
return 0;
}
if (k == 1) {
return 1;
}
return getKLevelNodeCount(root.left, k - 1) + getKLevelNodeCount(root.right, k - 1);
}
// 获取二叉树的高度
int getHeight(TreeNode root) {
if (root == null) {
return 0;
}
return Math.max(getHeight(root.left), getHeight(root.right)) + 1;
}
// 检测值为value的元素是否存在
TreeNode findVal(TreeNode root, char val) {
if (root == null) return null;
if (root.val == val) return root;
TreeNode ret = findVal(root.left, val);
if (ret != null) {
return ret;
}
ret = findVal(root.right, val);
if (ret != null) {
return ret;
}
return null;
}
/**
* 是否为完全二叉树
*
* @param root 根节点
* @return
*/
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 {
break;
}
}
while (!queue.isEmpty()) {
TreeNode top = queue.peek();
if (top != null) {
return false;
}
queue.poll();
}
return true;
}
public boolean isCompleteTreeOJ(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) {
break;
}
if (cur.left != null) {
queue.offer(cur.left);
}
if (cur.right != null) {
queue.offer(cur.right);
}
}
while (!queue.isEmpty()) {
TreeNode ret = queue.poll();
if (ret != null) {
return false;
}
}
return true;
}
TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
if (root1 == null) {
return root2;
}
if (root2 == null) {
return root1;
}
// root1.val=root1.val+root2.val;
root1.left = mergeTrees(root1.left, root2.left);
root1.right = mergeTrees(root1.right, root2.right);
return root1;
}
private boolean isSameTree(TreeNode p, TreeNode q) {
if (p == null && q != null || p != null && q == null) {
return false;
}
if (p == null && q == null) {
return true;
}
if (p.val != q.val) {
return false;
}
return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
}
public boolean isSubtree(TreeNode root, TreeNode subRoot) {
if (root == null || subRoot == null) {
return false;
}
if (isSameTree(root, subRoot)) {
return true;
}
if (isSameTree(root.left, subRoot)) {
return true;
}
if (isSameTree(root.right, subRoot)) {
return true;
}
return false;
}
public boolean isSymmetricChild(TreeNode left, TreeNode right) {
if (left == null && right == null) {
return true;
}
if (left == null || right == null || left.val != right.val) {
return false;
}
return isSymmetricChild(left.left, right.right) && isSymmetricChild(left.right, right.left);
}
public boolean isSymmetric(TreeNode root) {
if (root == null) {
return true;
}
return isSymmetricChild(root.left, root.right);
}
// 解法1:根据二叉搜索树的思路
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
//LCA问题
if (root == null) {
return root;
}
if (root == p || root == q) {
return root;
}
TreeNode left = lowestCommonAncestor(root.left, p, q);
TreeNode right = lowestCommonAncestor(root.right, p, q);
if (left != null && right != null) {
return root;
} else if (left != null) {
return left;
} else if (right != null) {
return right;
}
return null;
}
// 解法二 根据栈 路径思路
/**
* 把root到node的路径放到栈里面
*
* @param root 根节点
* @param node 需要找的节点
* @param stack 存放路径的栈
* @return
*/
public boolean getPath(TreeNode root, TreeNode node, Stack<TreeNode> stack) {
if (root == null || node == null) {
return false;
}
stack.push(root);
if (root == node) {
return true;
}
boolean flg = getPath(root.left, node, stack);
if (flg == true) {
return true;
}
flg = getPath(root.right, node, stack);
if (flg == true) {
return true;
}
stack.pop();
return false;
}
public TreeNode lowestCommonAncestor1(TreeNode root, TreeNode p, TreeNode q) {
if (root == null) {
return null;
}
Stack<TreeNode> stack1 = new Stack<>();
Stack<TreeNode> stack2 = new Stack<>();
getPath(root, p, stack1);
getPath(root, q, stack2);
int size1 = stack1.size();
int size2 = stack2.size();
if (size1 > size2) {
int size = size1 - size2;
while (size != 0) {
stack1.pop();
size--;
}
while (!stack1.empty() && !stack2.empty()) {
if (stack1.pop() == stack2.pop()) {
return stack1.pop();
} else {
stack1.pop();
stack2.pop();
}
}
}
if (size2 > size1) {
int size = size2 - size1;
while (size != 0) {
stack2.pop();
size--;
}
while (!stack1.empty() && !stack2.empty()) {
if (stack1.pop() == stack2.pop()) {
return stack1.pop();
} else {
stack1.pop();
stack2.pop();
}
}
}
return null;
}
// 二叉搜素树转换为排好序的双向链表
/*TreeNode prev=null;
public void inorder(TreeNode pCur){
if (pCur==null){
return;
}
inorder(pCur.left);
pCur.left=prev;
if (prev!=null){
prev.right=pCur;
}
prev=pCur;
inorder(pCur.right);
}
public TreeNode Convert(TreeNode pRootOfTree) {
if (pRootOfTree==null){
return null ;
}
inorder(pRootOfTree);
while (pRootOfTree.left!=null){
pRootOfTree=pRootOfTree.left;
}
return pRootOfTree;
}*/
TreeNode prev = null;
public void inorderOJ(TreeNode root) {
if (root == null) {
return;
}
inorderOJ(root.left);
root.left = prev;
if (prev != null) {
prev.right = root;
}
prev = root;
inorderOJ(root.right);
}
public TreeNode Convert(TreeNode root) {
if (root == null) {
return null;
}
while (root.left != null) {
root = root.left;
}
return root;
}
//根据前序遍历和中序遍历来创建二叉树
public int preIndex = 0;
public TreeNode createTreeByPandI(int[] preorder, int[] inorder, int inbegin, int inend) {
if (inbegin > inend) {
return null;
}
TreeNode root = new TreeNode(preorder[preIndex]);
int rootIndex = findIndexOfI(inorder, inbegin, inend, preorder[preIndex]);
if (rootIndex == -1) {
return null;
}
preIndex++;
root.left = createTreeByPandI(preorder, inorder, inbegin, rootIndex - 1);
root.right = createTreeByPandI(preorder, inorder, rootIndex + 1, inend);
return root;
}
private int findIndexOfI(int[] inoder, int inbegin, int inend, int key) {
for (int j = inbegin; j <= inend; j++) {
if (inoder[j] == key) {
return j;
}
}
return -1;
}
public TreeNode buildTree(int[] preorder, int[] inorder) {
if (preorder == null || inorder == null) {
return null;
}
return createTreeByPandI(preorder, inorder, 0, inorder.length - 1);
}
//根据后序遍历和中序遍历来创建二叉树
public int postIndex = 0;
public TreeNode createTreeByPandI(int[] inorder, int[] postorder, int inbegin, int inend) {
if (inbegin > inend) {
return null;
}
TreeNode root = new TreeNode(postorder[postIndex]);
int rootIndex = findIndexOfI(inorder, inbegin, inend, postorder[postIndex]);
if (rootIndex == -1) {
return null;
}
preIndex--;
root.right = createTreeByPandI(inorder, postorder, rootIndex + 1, inend);
root.left = createTreeByPandI(inorder, postorder, inbegin, rootIndex - 1);
return root;
}
private int findIndexOfI(int[] inoder, int inbegin, int inend, int key) {
for (int j = inbegin; j <= inend; j++) {
if (inoder[j] == key) {
return j;
}
}
return -1;
}
public TreeNode buildTree(int[] inorder, int[] postorder) {
if (postorder == null || inorder == null) {
return null;
}
postIndex = postorder.length - 1;
return createTreeByPandI(inorder, postorder, 0, inorder.length - 1);
}
// 二叉树创建字符串.
public void trerToString(TreeNode root, StringBuilder sb) {
if (root == null) {
return;
}
sb.append(root.val);
if (root.left != null) {
sb.append("(");
trerToString(root.left, sb);
sb.append(")");
} else {
if (root.right == null) {
return;
} else {
sb.append("()");
}
}
if (root.right == null) {
return;
} else {
sb.append("(");
trerToString(root.right, sb);
sb.append(")");
}
}
public String tree2str(TreeNode root) {
if (root == null) {
return null;
}
StringBuilder sb = new StringBuilder();
trerToString(root, sb);
return sb.toString();
}
public TreeNode increasingBST(TreeNode root) {
if (root == null) {
return null;
}
List<Integer> list = new ArrayList<>();
inorderBST(root, list);
TreeNode prevNode = new TreeNode(-1);
TreeNode rightNode = prevNode;
for (int val : list) {
rightNode.right = new TreeNode(val);
rightNode = rightNode.right;
}
return prevNode.right;
}
public void inorderBST(TreeNode root, List<Integer> list) {
if (root == null) {
return;
}
inorderBST(root.left, list);
list.add(root.val);
inorderBST(root.right, list);
}
//前序遍历非递归实现
public List<Integer> preorderTraversal(TreeNode root) {
List<Integer> ret = new ArrayList<>();
Stack<TreeNode> stack = new Stack<>();
TreeNode cur = root;
while (cur != null || !stack.empty()) {
while (cur != null) {
stack.push(cur);
ret.add(cur.val);
cur = cur.left;
}
TreeNode top = stack.pop();
cur = top.right;
}
return ret;
}
//中序遍历非递归实现
public List<Integer> inorderTraversal(TreeNode root) {
List<Integer> ret = new ArrayList<>();
Stack<TreeNode> stack = new Stack<>();
TreeNode cur = root;
while (cur != null || !stack.empty()) {
while (cur != null) {
stack.push(cur);
cur = cur.left;
}
TreeNode top = stack.pop();
ret.add(top.val);
cur = top.right;
}
return ret;
}
//后续遍历非递归实现
public List<Integer> postorderTraversal(TreeNode root) {
List<Integer> ret = new ArrayList<>();
Stack<TreeNode> stack = new Stack<>();
TreeNode cur = root;
TreeNode prev=null;
while (cur != null || !stack.empty()) {
while (cur != null) {
stack.push(cur);
cur = cur.left;
}
TreeNode top = stack.peek();
if (top.right == null || top.right==prev) { //如果当前节点的右子树被打印过了,直接就可以弹出了
stack.pop();
ret.add(top.val);
prev=top; //记录一下 最后一次打印的节点
} else {
cur = top.right;
}
}
return ret;
}
}
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