update

hard/864.shortest-path-to-get-all-keys.java

@@ -0,0 +1,62 @@
+import java.util.LinkedList;
+
+class Solution {
+    class Node implements Comparable<Node> {
+        int keys;
+        int step;
+        int y;
+        int x;
+
+        Node(int keys, int step, int y, int x) {
+            this.keys = keys;
+            this.step = step;
+            this.y = y;
+            this.x = x;
+        }
+    }
+
+    int m;
+    int n;
+    int acc;
+    char[][] map;
+
+    final int[] dy = new int[]{0, 1, 0, -1};
+    final int[] dx = new int[]{1, 0, -1, 0};
+
+    public int shortestPathAllKeys(String[] grid) {
+        if ((m = grid.length) == 0 || (n = grid[0].length()) == 0) return -1;
+        LinkedList<Node> queue = new LinkedList<>();
+        map = new char[m][n];
+        for (int i = 0; i < m; i++) {
+            map[i] = grid[i].toCharArray();
+            for (int j = 0; j < n; j++) {
+                char ch = map[i][j];
+                if (ch == '@') queue.offer(new Node(0, 0, i, j));
+                if ('a' <= ch && ch <= 'f') acc |= 1 << (ch - 'a');
+            }
+        }
+        boolean[][][] used = new boolean[m][n][1 << 6];
+        while (!queue.isEmpty()) {
+            Node top = queue.poll();
+            if (!isValidMove(top, used)) continue;
+            used[top.y][top.x][top.keys] = true;
+            char ch = map[top.y][top.x];
+            if ('a' <= ch && ch <= 'f') top.keys |= 1 << (ch - 'a');
+            if (top.keys == acc) return top.step;
+            for (int i = 0; i < 4; i++) {
+                Node next = new Node(top.keys, top.step + 1, top.y + dy[i], top.x + dx[i]);
+                queue.offer(next);
+            }
+        }
+        return -1;
+    }
+
+    private boolean isValidMove(Node node, boolean[][][] used) {
+        if (node.y < 0 || m <= node.y || node.x < 0 || n <= node.x) return false; // Out of map
+        if (used[node.y][node.x][node.keys]) return false; // Visited
+        char ch = map[node.y][node.x];
+        if (ch == '#') return false; // Wall
+        if ('A' <= ch && ch <= 'F') return ((1 << (ch - 'A')) & node.keys) != 0; // Has no key
+        return true;
+    }
+}