Hi guys, I wrote a straight forward BFS solution to solve 1B Expogo
question, targeting to solve test set 1 and 2.
However, not knowing which corner case it fails, the solution got WA.
Basic cases are all past locally, anyone could advise why below solution
fails?
import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
public class Solution {
private static final int LIMIT = 400; // target at set 2: limit 100,
loosen a bit
private static final int[][] dirs = {{0,1},{0,-1},{1,0},{-1,0}};
private static final String[] ways = {"N", "S", "E", "W"};
private static String solve(int x, int y) {
int maxStep = (int) (Math.log(LIMIT) / Math.log(2) + 1);
Queue<int[]> queue = new LinkedList<>();
boolean[][] visited = new boolean[2*LIMIT+1][2*LIMIT+1];
String[][] paths = new String[2*LIMIT+1][2*LIMIT+1];
for (String[] path : paths) Arrays.fill(path, "");
queue.offer(new int[]{0, 0});
//visited[LIMIT][LIMIT] = true; // let (0, 0) output IMPOSSIBLE
int step = 0, dist;
while (!queue.isEmpty() && step <= maxStep + 3) { // loosen a bit
int size = queue.size();
dist = (int) Math.pow(2, step);
for (int s = 0; s < size; s++) {
int[] cell = queue.poll();
if (step > 0 && cell[0] == x && cell[1] == y) return
paths[x+LIMIT][y+LIMIT]; // let (0, 0) output IMPOSSIBLE
for (int i = 0; i < 4; i++) {
int xx = cell[0] + dirs[i][0] * dist;
int yy = cell[1] + dirs[i][1] * dist;
if (xx >= -LIMIT && xx <= LIMIT && yy >= -LIMIT && yy
<= LIMIT && !visited[xx+LIMIT][yy+LIMIT]) {
visited[xx+LIMIT][yy+LIMIT] = true;
queue.offer(new int[]{xx, yy});
paths[xx+LIMIT][yy+LIMIT] =
paths[cell[0]+LIMIT][cell[1]+LIMIT] + ways[i];
}
}
}
step++;
}
return "IMPOSSIBLE";
}
public static void main(String[] args) {
Scanner in = new Scanner((System.in));
int T = in.nextInt(); // Scanner has functions to read ints, longs,
strings, chars, etc.
for (int ks = 1; ks <= T; ++ks) {
int x = in.nextInt();
int y = in.nextInt();
System.out.println("Case #" + ks + ": " + solve(x, y));
}
}
}
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