1559. Detect Cycles in 2D Grid

Given a 2D array of characters grid of size m x n, you need to find if there exists any cycle consisting of the same value in grid.

A cycle is a path of length 4 or more in the grid that starts and ends at the same cell. From a given cell, you can move to one of the cells adjacent to it - in one of the four directions (up, down, left, or right), if it has the same value of the current cell.

Also, you cannot move to the cell that you visited in your last move. For example, the cycle (1, 1) -> (1, 2) -> (1, 1) is invalid because from (1, 2) we visited (1, 1) which was the last visited cell.

Return true if any cycle of the same value exists in grid, otherwise, return false.

Example 1:

Input: grid = [["a","a","a","a"],["a","b","b","a"],["a","b","b","a"],["a","a","a","a"]]
Output: true
Explanation: There are two valid cycles shown in different colors in the image below:
![](https://assets.leetcode.com/uploads/2020/07/15/11.png)

Example 2:

Input: grid = [["c","c","c","a"],["c","d","c","c"],["c","c","e","c"],["f","c","c","c"]]
Output: true
Explanation: There is only one valid cycle highlighted in the image below:
![](https://assets.leetcode.com/uploads/2020/07/15/2.png)

Example 3:

Input: grid = [["a","b","b"],["b","z","b"],["b","b","a"]]
Output: false

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m <= 500
• 1 <= n <= 500
• grid consists only of lowercase English letters.

# @lc code=start
using LeetCode

function contains_cycle(grid::Vector{Vector{String}})
    dirs = ((1, 0, 3), (-1, 0, 0), (0, 1, 1), (0, -1, 2))
    function bfs(grid::Vector{Vector{String}}, r::Int, c::Int)
        sym = grid[r][c]
        q_pos = Queue{Pair{Int, Int}}()
        q_dir = Queue{Int}()
        enqueue!(q_pos, Pair(r, c))
        enqueue!(q_dir, 0)
        visited[r, c] = true
        while !isempty(q_pos)
            pos = dequeue!(q_pos)
            dir = dequeue!(q_dir)
            for d in dirs
                nx, ny = pos.first + d[1], pos.second + d[2]
                if 0 < nx <= nr && 0 < ny <= nc && dir != d[3] && sym == grid[nx][ny]
                    if visited[nx, ny]
                        return true
                    else
                        visited[nx, ny] = true
                        enqueue!(q_pos, Pair(nx, ny))
                        enqueue!(q_dir, 3 - d[3])
                    end
                end
            end
        end
        false
    end
    nr, nc = length(grid), length(grid[1])
    visited = fill(false, nr, nc)
    for r in 1 : nr
        for c in 1 : nc
            if !visited[r, c] && bfs(grid, r, c)
                # println(grid[r][c])
                return true
            end
        end
    end
    return false
end
# @lc code=end

contains_cycle (generic function with 1 method)

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