Path Finder 2: Electric Boogaloo

View as PDF

Submit solution

Points: 15 (partial)
Time limit: 2.0s
Memory limit: 256M

Authors:
Problem type

You are given an N×M grid with K blocked squares and the others open. From an open square, you may move to any other open square that shares an edge with your current square. For Q queries of 4 integers ra,ca,rb,cb, please determine whether there is a path from (ra,ca) to (rb,cb).

Constraints

For all subtasks:

1N,M,Q5×105

0K5×105

1ri,ra,rbN

1ci,ca,cbM

Each given blocked square is unique, and for all queries the squares (ra,ca) and (rb,cb) will not be blocked.

Subtask 1 [20%]

1N,M2×103

Subtask 2 [80%]

No additional constraints.

Input Specification

The first line will contain 4 integers N, M, K, and Q.

The next K lines will each contain 2 integers ri and ci, representing that square (ri,ci) is blocked.

The following Q lines will each contain 4 integers ra,ca,rb,cb, representing a query from (ra,ca) to (rb,cb).

Output Specification

For each query, output one line containing YES if it is possible to reach (rb,cb) from (ra,ca), or NO otherwise.

Sample Input 1

Copy
5 5 11 1
2 2
4 2
3 2
2 3
5 2
3 1
1 5
3 5
2 5
4 5
4 4
1 1 5 5

Sample Output 1

Copy
YES

Explanation for Sample 1

The following is a diagram for the grid given in Sample 1 (. marks open squares, while # marks blocked squares):

Copy
....#
.##.#
##..#
.#.##
.#...

It can be shown that there is a path from (1,1) to (5,5) in the grid above.

Sample Input 2

Copy
5 5 9 3
5 1
1 2
1 5
3 2
2 3
5 3
3 3
3 5
4 4
1 1 5 5
2 1 4 3
2 5 2 5

Sample Output 2

Copy
NO
YES
YES

Explanation for Sample 2

The following is a diagram for the grid given in Sample 2 (. marks open squares, while # marks blocked squares):

Copy
.#..#
..#..
.##.#
...#.
#.#..

Comments


  • 0
    stanwww  commented on Dec. 6, 2024, 4:03 a.m.

    What is the intended solution for this problem? I need hints.