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-rw-r--r--snakes_ladders.c82
-rw-r--r--snakes_ladders.py65
2 files changed, 147 insertions, 0 deletions
diff --git a/snakes_ladders.c b/snakes_ladders.c
new file mode 100644
index 0000000..b7128db
--- /dev/null
+++ b/snakes_ladders.c
@@ -0,0 +1,82 @@
+// 909. Snakes and Ladders
+#include "leetcode.h"
+
+/*
+ * you are given an 'n x n' integer matrix 'board' where the cells are all
+ * labeled from 1 to 'n^2' in 'boustropheden style' starting from bottom left of
+ * the board, and alternating direction each row. a board square on row 'r' and
+ * column 'c' has a snake of a ladder if 'board[r][c] != -1'. the destination of
+ * that snake or ladder is 'board[r][c]'. squares 1 and 'n^2' are not the
+ * starting points of any snake or ladder. note that you only take a snake or a
+ * ladder at most once per dice roll. if the destination to a snake or ladder is
+ * the start of another snake or ladder, you do not follow the subsequent snake
+ * or ladder.
+ */
+
+struct queue {
+ int num;
+ int moves;
+};
+
+void coordinates(int num, int n, int *row, int *col) {
+ int r = (num - 1) / n, c = (num - 1) % n;
+ if (r % 2 == 1)
+ c = n - 1 - c;
+ *row = n - 1 - r;
+ *col = c;
+}
+
+int snakesAndLadders(int **board, int boardSize, int *boardColSize) {
+ int n = boardSize * boardSize, front = 0, rear = 0;
+ bool *vis = (bool *)calloc(n + 1, sizeof(bool));
+ struct queue *q = (struct queue *)malloc(n * sizeof(struct queue));
+ q[rear].num = 1;
+ q[rear++].moves = 0;
+ vis[1] = true;
+ while (front < rear) {
+ struct queue curr = q[front++];
+ if (curr.num == n) {
+ free(vis);
+ free(q);
+ return curr.moves;
+ }
+ for (int i = 1; i <= 6; i++) {
+ int next = curr.num + 1;
+ if (next > n)
+ continue;
+ int row, col;
+ coordinates(next, boardSize, &row, &col);
+ if (board[row][col] != -1)
+ next = board[row][col];
+ if (next == n) {
+ free(vis);
+ free(q);
+ return curr.moves + 1;
+ }
+ if (!vis[next]) {
+ vis[next] = true;
+ q[rear].num = next;
+ q[rear++].moves = curr.moves + 1;
+ }
+ }
+ }
+ free(vis);
+ free(q);
+ return -1;
+}
+
+int main() {
+ int b1i[6][6] = {{-1, -1, -1, -1, -1, -1}, {-1, -1, -1, -1, -1, -1},
+ {-1, -1, -1, -1, -1, -1}, {-1, 35, -1, -1, 13, -1},
+ {-1, -1, -1, -1, -1, -1}, {-1, 15, -1, -1, -1, -1}};
+ int b2i[2][2] = {{-1, -1}, {-1, 3}};
+ struct two_d_arr b1, b2;
+ two_d_arr_init(&b1, ARRAY_SIZE(b1i), ARRAY_SIZE(b1i[0]), b1i);
+ two_d_arr_init(&b2, ARRAY_SIZE(b2i), ARRAY_SIZE(b2i[0]), b2i);
+ printf("%d\n",
+ snakesAndLadders(b1.arr, b1.row_size, b1.col_size)); // expect: 4
+ printf("%d\n",
+ snakesAndLadders(b2.arr, b2.row_size, b2.col_size)); // expect: 1
+ two_d_arr_free(&b1);
+ two_d_arr_free(&b2);
+}
diff --git a/snakes_ladders.py b/snakes_ladders.py
new file mode 100644
index 0000000..5541d87
--- /dev/null
+++ b/snakes_ladders.py
@@ -0,0 +1,65 @@
+# 909. Snakes and Ladders
+
+"""
+you are given an 'n x n' integer matrix 'board' where the cells are all
+labeled from 1 to 'n^2' in 'boustropheden style' starting from bottom left of
+the board, and alternating direction each row. a board square on row 'r' and
+column 'c' has a snake of a ladder if 'board[r][c] != -1'. the destination of
+that snake or ladder is 'board[r][c]'. squares 1 and 'n^2' are not the
+starting points of any snake or ladder. note that you only take a snake or a
+ladder at most once per dice roll. if the destination to a snake or ladder is
+the start of another snake or ladder, you do not follow the subsequent snake
+or ladder.
+"""
+
+
+class Solution(object):
+ def snakesAndLadders(self, board):
+ """
+ :type board: List[List[int]]
+ :rtype: int
+ """
+ n = len(board)
+
+ def coordinates(num):
+ row, col = (num - 1) // n, (num - 1) % n
+ col = n - 1 if row % 2 == 1 else col
+ row = n - 1 - row
+ return row, col
+
+ vis, queue = set(), [(1, 0)]
+ vis.add(1)
+ while queue:
+ curr, moves = queue.pop(0)
+ if curr == n**2:
+ return moves
+ for i in range(1, 7):
+ next = curr + i
+ if next > n**2:
+ continue
+ row, col = coordinates(next)
+ if board[row][col] != -1:
+ next = board[row][col]
+ if next == n**2:
+ return moves + 1
+ if next not in vis:
+ vis.add(next)
+ queue.append((next, moves + 1))
+ return -1
+
+
+if __name__ == "__main__":
+ obj = Solution()
+ print(
+ obj.snakesAndLadders(
+ board=[
+ [-1, -1, -1, -1, -1, -1],
+ [-1, -1, -1, -1, -1, -1],
+ [-1, -1, -1, -1, -1, -1],
+ [-1, 35, -1, -1, 13, -1],
+ [-1, -1, -1, -1, -1, -1],
+ [-1, 15, -1, -1, -1, -1],
+ ]
+ )
+ )
+ print(obj.snakesAndLadders(board=[[-1, -1], [-1, 3]]))