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Utils.java

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package utils;

import java.sql.Array;

import java.util.ArrayList;

import java.util.LinkedList;

import java.util.List;

import java.util.Queue;

import java.util.stream.Collectors;

public class Utils {

public static void swap(int[] a, int i, int j) {

int temp = a[i];

a[i] = a[j];

a[j] = temp;

}

public static String treeToStr(TreeNode root) {

if(root==null) return "";

List res=new ArrayList();

LinkedList<TreeNode> qu=new LinkedList<>();

qu.addFirst(root);

while(!qu.isEmpty()){

TreeNode node=qu.removeLast();

if(node==null){

res.add("null");

continue;

}else{

res.add(node.val);

qu.addFirst(node.left);

qu.addFirst(node.right);

}

}

StringBuilder r=new StringBuilder();

for (int i = 0; i < res.size(); i++) {

r.append(res.get(i));

if(i<res.size()-1) r.append(",");

}

return r.toString();

}

public static TreeNode createTree(String data) {

if(data.length()==0) return null;

String[] req=data.split(",");

LinkedList<TreeNode> qu=new LinkedList<>();

TreeNode root=new TreeNode(Integer.parseInt(req[0]));

qu.addFirst(root);

int index=1;

while(index<req.length){

TreeNode node=qu.removeLast();

if(!("null".equals(req[index]))){

node.left=new TreeNode(Integer.parseInt(req[index]));

qu.addFirst(node.left);

}

index++;

if(!("null".equals(req[index]))){

node.right=new TreeNode(Integer.parseInt(req[index]));

qu.addFirst(node.right);

}

index++;

}

return root;

}

public static String printTree(TreeNode root) {

if(root==null) return "";

int depth = maxDepth(root);

List<List<String>> res=new ArrayList<>();

Queue<TreeNode> qu=new LinkedList<>();

qu.offer(root);

int flag = 1;

while(!qu.isEmpty()){

int size = qu.size();

List<String> tmp = new ArrayList<>();

for (int i = 0; i < size; i++) {

TreeNode node=qu.poll();

if(node==null){

tmp.add("null");

}else{

tmp.add(node.val + "");

if (node.left != null || flag < depth) qu.offer(node.left);

if (node.right != null || flag < depth) qu.offer(node.right);

}

}

flag ++;

res.add(tmp);

}

StringBuilder r=new StringBuilder();

for (int i = 0; i < res.size(); i++) {

r.append(String.join(",", res.get(i))).append("\r\n");

}

return r.toString();

}

public static int maxDepth(TreeNode root) {

if (root == null) {

return 0;

} else {

int leftHeight = maxDepth(root.left);

int rightHeight = maxDepth(root.right);

return Math.max(leftHeight, rightHeight) + 1;

}

}

public static ListNode createList(String data) {

if(data.length()==0) return null;

String[] req=data.split(",");

ListNode head = new ListNode(Integer.parseInt(req[0]));

ListNode dummy = new ListNode(-1, head);

for (int i = 1; i < req.length; i++) {

head.next = new ListNode(Integer.parseInt(req[i]));

head = head.next;

}

return dummy.next;

}

public static String printList(ListNode head) {

ListNode node = head;

List<Integer> list = new ArrayList<>();

while (node != null) {

list.add(node.val);

node = node.next;

}

return list.toString();

}

}