Add Java solution 909. Snakes and Ladders

java/0909-snakes-and-ladders.java

@@ -0,0 +1,52 @@
+class Solution {
+ public int snakesAndLadders(int[][] board) {
+ int n = board.length;
+
+ reverseBoard(board);
+
+ boolean[] visited = new boolean[n*n+1];
+ Queue<int[]> q = new LinkedList<>();
+ q.offer(new int[]{1, 0});
+ visited[1] = true;
+
+ while(!q.isEmpty()) {
+ int[] curr = q.poll();
+ for(int j=1; j<=6; j++) {
+ int next = curr[0] + j;
+ int[] coor = squareToCoor(next, n);
+ if(board[coor[0]][coor[1]] != -1) {
+ next = board[coor[0]][coor[1]];
+ }
+ if(next == n*n) {
+ return curr[1] + 1;
+ }
+ if(!visited[next]) {
+ visited[next] = true;
+ q.offer(new int[]{next, curr[1] + 1});
+ }
+ }
+ }
+
+ return -1;
+ }
+
+ public int[] squareToCoor(int square, int n) {
+ int row = (square - 1) / n;
+ int col = (square - 1) % n;
+ if(row % 2 != 0) {
+ col = n - 1 - col;
+ }
+ return new int[]{row, col};
+ }
+
+ public void reverseBoard(int[][] board) {
+ int l = 0, r = board.length-1;
+ while(l < r) {
+ int[] temp = board[l];
+ board[l] = board[r];
+ board[r] = temp;
+ l++;
+ r--;
+ }
+ }
+}