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// 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);
}
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