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solves #1091: Shortest Path in Binary Matrix in java
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‎README.md

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| 1085 | 🔒 [Sum of Digits in Minimum Number](https://leetcode.com/problems/sum-of-digits-in-the-minimum-number) | | |
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| 1086 | 🔒 [High Five](https://leetcode.com/problems/high-five) | | |
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| 1089 | [Duplicate Zeroes](https://leetcode.com/problems/duplicate-zeros) | [![Java](assets/java.png)](src/DuplicateZeros.java) | |
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| 1091 | [Shortest Path in Binary Matrix](https://leetcode.com/problems/shortest-path-in-binary-matrix) | [![Java](assets/java.png)](src/ShortestPathInBinaryMatrix.java) | |
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| 1099 | 🔒 [Two Sum Less Than K](https://leetcode.com/problems/two-sum-less-than-k) | | |
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| 1101 | [The Earliest Moment When Everyone Become Friend](https://leetcode.com/problems/the-earliest-moment-when-everyone-become-friends) | [![Java](assets/java.png)](src/TheEarliestMomentWhenEveryoneBecomeFriends.java) | |
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| 1103 | [Distribute Candies to People](https://leetcode.com/problems/distribute-candies-to-people) | [![Java](assets/java.png)](src/DistributeCandiesToPeople.java) | |

‎src/HelloWorld.java

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// T: O(N + E alp(N))
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// S: O(N)
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import java.security.cert.Certificate;
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import java.util.LinkedList;
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import java.util.Queue;
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public class HelloWorld {
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private static final class DisjointSet {
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private final int[] roots, rank;
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public DisjointSet(int size) {
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roots = new int[size];
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rank = new int[size];
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for (int i = 0 ; i < size ; i++) {
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roots[i] = i;
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rank[i] = 1;
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}
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public static class Node {
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public int val;
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public Node left;
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public Node right;
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public Node next;
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public Node() {}
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public Node(int _val) {
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val = _val;
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}
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public int find(int num) {
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if (num == roots[num]) {
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return num;
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}
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return roots[num] = find(roots[num]);
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public Node(int _val, Node _left, Node _right, Node _next) {
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val = _val;
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left = _left;
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right = _right;
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next = _next;
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}
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};
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public boolean areConnected(int x, int y) {
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return find(x) == find(y);
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public Node connect(Node root) {
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if (root == null) {
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return null;
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}
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public void union(int x, int y) {
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final int rootX = find(x), rootY = find(y);
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if (rootX == rootY) {
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return;
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final Queue<Node> queue = new LinkedList<>();
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queue.add(root);
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queue.add(null);
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Node current = null;
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while (!queue.isEmpty()) {
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final Node node = queue.poll();
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if (node == null) {
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if (!queue.isEmpty()) {
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queue.add(null);
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current = null;
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}
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continue;
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}
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if (rank[rootX] > rank[rootY]) {
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roots[rootY] = rootX;
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} else if (rank[rootX] < rank[rootY]) {
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roots[rootX] = rootY;
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} else {
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roots[rootY] = rootX;
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rank[rootX]++;
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addChildrenToQueue(queue, node);
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if (current != null) {
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current.next = node;
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}
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current = node;
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}
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return root;
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}
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public boolean validPath(int n, int[][] edges, int source, int destination) {
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final DisjointSet disjointSet = new DisjointSet(n);
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for (int[] edge : edges) {
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disjointSet.union(edge[0], edge[1]);
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}
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return disjointSet.areConnected(source, destination);
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private static void addChildrenToQueue(Queue<Node> queue, Node node) {
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if (node.left != null) queue.add(node.left);
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if (node.right != null) queue.add(node.right);
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}
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}

‎src/ShortestPathInBinaryMatrix.java

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// https://leetcode.com/problems/shortest-path-in-binary-matrix
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// N = total number of vertices
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// T: O(N)
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// S: O(N)
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import java.util.ArrayList;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Queue;
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public class ShortestPathInBinaryMatrix {
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private static final List<List<Integer>> directions = List.of(
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List.of(-1, -1),
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List.of(-1, 0),
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List.of(-1, 1),
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List.of(1, -1),
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List.of(1, 0),
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List.of(1, 1),
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List.of(0, -1),
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List.of(0, 1)
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);
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public int shortestPathBinaryMatrix(int[][] grid) {
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final int n = grid.length;
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if (grid[0][0] == 1 || grid[n - 1][n - 1] == 1) {
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return -1;
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}
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final Queue<int[]> queue = new LinkedList<>();
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queue.add(new int[] {0, 0});
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grid[0][0] = 1;
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while (!queue.isEmpty()) {
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final int[] position = queue.poll();
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if (position[0] == n - 1 && position[1] == n - 1) {
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return grid[n - 1][n - 1];
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}
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for (int[] neighbour : getNeighbours(position, grid)) {
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queue.add(neighbour);
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grid[neighbour[0]][neighbour[1]] = grid[position[0]][position[1]] + 1;
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}
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}
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return -1;
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}
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private static List<int[]> getNeighbours(int[] position, int[][] grid) {
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final List<int[]> result = new ArrayList<>();
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for (List<Integer> direction : directions) {
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final int row = position[0] + direction.get(0);
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final int column = position[1] + direction.get(1);
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if (isValid(grid, row, column) && grid[row][column] == 0) {
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result.add(new int[] { row, column });
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}
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}
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return result;
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}
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private static boolean isValid(int[][] grid, int row, int column) {
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final int n = grid.length;
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return row >= 0 && row < n && column >= 0 && column < n;
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}
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}

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