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‎leetcode-algorithms/README.md

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|454|[4Sum II](https://leetcode.com/problems/4sum-ii/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/_4SumII.java) | O(n) |O(n) | Medium| HashMap
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|453|[Minimum Moves to Equal Array Elements](https://leetcode.com/problems/minimum-moves-to-equal-array-elements/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/MinimumMovestoEqualArrayElements.java)| O(n)|O(1) | Easy|
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|451|[Sort Characters By Frequency](https://leetcode.com/problems/sort-characters-by-frequency/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SortCharactersByFrequency.java) | O(nlogn) |O(n) | Medium| HashMap
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|449|[Serialize and Deserialize BST](https://leetcode.com/problems/serialize-and-deserialize-bst/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SerializeandDeserializeBST.java)| O(n)|O(h) | Medium| BFS
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|448|[Find All Numbers Disappeared in an Array](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindAllNumbersDisappearedinanArray.java)| O(n)|O(1) | Easy| Array, HashMap
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|447|[Number of Boomerangs](https://leetcode.com/problems/number-of-boomerangs/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/NumberofBoomerangs.java)| O(n^2)|O(n) | Easy| HashMap
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|442|[Find All Duplicates in an Array](https://leetcode.com/problems/find-all-duplicates-in-an-array/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindAllDuplicatesinanArray.java)| O(n)|O(1) | Medium| Array
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|301|[Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/RemoveInvalidParentheses.java)| ? | ? | Hard| BFS
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|299|[Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/BullsandCows.java)| O(n)|O(1) | Easy|
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|298|[Binary Tree Longest Consecutive Sequence](https://leetcode.com/problems/binary-tree-longest-consecutive-sequence/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/BinaryTreeLongestConsecutiveSequence.java)| O(n)|O(n) | Medium | Tree
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|297|[Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SerializeandDeserializeBinaryTree.java)| ?|? | Hard|
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|297|[Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SerializeandDeserializeBinaryTree.java)| O(n) | O(h) | Hard| BFS
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|296|[Best Meeting Point](https://leetcode.com/problems/best-meeting-point/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/BestMeetingPoint.java)| ?|? | Hard|
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|295|[Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindMedianFromDataStream.java)| O(nlogn) | O(n) | Hard| Heap
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|294|[Flip Game II](https://leetcode.com/problems/flip-game-ii/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FlipGameII.java)| ? | ?| Medium| Backtracking

‎leetcode-algorithms/src/main/java/com/stevesun/common/classes/TreeNode.java

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public int val;
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public TreeNode left;
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public TreeNode right;
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@Override
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public String toString() {
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return "TreeNode{" +
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"val=" + val +
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", left=" + left +
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", right=" + right +
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'}';
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}
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public TreeNode(int x){this.val = x;}
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public TreeNode(TreeNode left, int val, TreeNode right) {

‎leetcode-algorithms/src/main/java/com/stevesun/solutions/SerializeandDeserializeBST.java

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package com.stevesun.solutions;
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import com.stevesun.common.classes.TreeNode;
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import java.util.LinkedList;
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import java.util.Queue;
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/**
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* Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.
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Design an algorithm to serialize and deserialize a binary search tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.
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The encoded string should be as compact as possible.
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Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
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*/
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public class SerializeandDeserializeBST {
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// Encodes a tree to a single string.
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public String serialize(TreeNode root) {
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Queue<TreeNode> queue = new LinkedList<>();
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StringBuilder stringBuilder = new StringBuilder();
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if (root == null) return stringBuilder.toString();
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queue.offer(root);
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while (!queue.isEmpty()) {
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int size = queue.size();
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for (int i = 0; i < size; i++) {
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TreeNode curr = queue.poll();
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if (curr == null) {
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stringBuilder.append("# ");
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} else {
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stringBuilder.append(curr.val + " ");
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queue.offer(curr.left);
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queue.offer(curr.right);
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}
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}
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}
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return stringBuilder.toString();
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}
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// Decodes your encoded data to tree.
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public TreeNode deserialize(String data) {
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if (data == null || data.length() == 0) return null;
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String[] nodes = data.split(" ");
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TreeNode root = new TreeNode(Integer.valueOf(nodes[0]));
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Queue<TreeNode> queue = new LinkedList<>();
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queue.offer(root);
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for (int i = 1; i < nodes.length; i++) {
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TreeNode curr = queue.poll();
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if (!nodes[i].equals("#")) {
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curr.left = new TreeNode(Integer.valueOf(nodes[i]));
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queue.offer(curr.left);
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}
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if (!nodes[++i].equals("#")) {
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curr.right = new TreeNode(Integer.valueOf(nodes[i]));
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queue.offer(curr.right);
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}
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}
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return root;
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}
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}

‎leetcode-algorithms/src/main/java/com/stevesun/solutions/SerializeandDeserializeBinaryTree.java

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then eventually just return the root.
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*/
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// Encodes a tree to a single string.
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public String serialize(TreeNode root) {
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if(root == null) return "";
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}
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return root;
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}
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}

‎leetcode-algorithms/src/test/java/com/stevesun/SerializeandDeserializeBSTTest.java

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package com.stevesun;
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import com.stevesun.common.classes.TreeNode;
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import com.stevesun.solutions.SerializeandDeserializeBST;
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import org.junit.Before;
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import org.junit.BeforeClass;
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import org.junit.Test;
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import static junit.framework.Assert.assertEquals;
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public class SerializeandDeserializeBSTTest {
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private static SerializeandDeserializeBST test;
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private static TreeNode actualRoot;
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private static TreeNode expectedRoot;
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@BeforeClass
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public static void setup(){
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test = new SerializeandDeserializeBST();
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}
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@Before
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public void setupForEachTest(){
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}
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@Test
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public void test1(){
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expectedRoot = new TreeNode(3);
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expectedRoot.left = new TreeNode(1);
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expectedRoot.right = new TreeNode(4);
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expectedRoot.left.right = new TreeNode(2);
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actualRoot = test.deserialize(test.serialize(expectedRoot));
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assertEquals(expectedRoot.toString(), actualRoot.toString());
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}
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}

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