Given a knight in a chessboard (a binary matrix with 0 as empty and 1 as barrier) with a source position, find the shortest path to a destination position, return the length of the route.
Return -1 if knight can not reached.
/** * Definition for a point. * public class Point { * publoc int x, y; * public Point() { x = 0; y = 0; } * public Point(int a, int b) { x = a; y = b; } * } */
public class Solution {
/** * @param grid a chessboard included 0 (false) and 1 (true) * @param source, destination a point * @return the shortest path */
public int shortestPath(boolean[][] grid, Point source, Point destination) {
if (grid == null || grid.length == 0 || grid[0].length == 0) {
return -1;
}
int n = grid.length;
int m = grid[0].length;
int[] directionX = {1, 1, -1, -1, 2, 2, -2, -2};
int[] directionY = {2, -2, 2, -2, 1, -1, 1, -1};
Queue<Point> queue = new LinkedList<>();
queue.offer(source);
int step = 0;
while (!queue.isEmpty()) {
int size = queue.size();
step++;
for (int i = 0; i < size; i++) {
Point point = queue.poll();
for (int j = 0; j < 8; j++) {
Point adj = new Point(
point.x + directionX[j],
point.y + directionY[j]
);
if (inBound(adj.x, adj.y, grid)) {
if (adj.x == destination.x && adj.y == destination.y) {
return step;
}
//走过的点不能再走了,抹掉
grid[adj.x][adj.y] = true;
queue.offer(adj);
}
}
}
}
return -1;
}
private boolean inBound(int x, int y, boolean[][] grid) {
int n = grid.length;
int m = grid[0].length;
return x >= 0 && x < n && y >= 0 && y < m && grid[x][y] == false;
}
}