请教一下大佬们二维矩阵的 DFS 问题，不知道为什么总是报错

业务场景：

有个二维矩阵 513 * 513 ，取值只有 0 或 1 ，根据值绘图，0 白色 1 黑色。 现在需要把不规则的黑色绘制成矩形，如下图：

代码如下：

func findConnectedRegion(matrix: [[Int]]) -> [[(Int, Int)]] {
        var result: [[(Int, Int)]] = []
        //    var visited: Set<(Int, Int)> = []
        var visited: Set<String> = []
        let numRows = matrix.count
        let numCols = matrix[0].count
        
        for i in 0..<matrix.count {
            for j in 0..<matrix[0].count {
                let position = (i, j)
                let str = String(i)+"-"+String(j)
                if matrix[i][j] == 1 && !visited.contains(str) {
                    var region: [(Int, Int)] = []
                    dfs(matrix: matrix, rows: numRows,cols: numCols,position: position, visited: visited, region: &region)
                    result.append(region)
                }
            }
        }
        
        return result
    }
    
    func dfs(matrix: [[Int]],rows:Int,cols:Int,position: (Int, Int), visited: Set<String>, region: inout [(Int, Int)]) {
//        let numRows = matrix.count
//        let numCols = matrix[0].count
        
        let numRows = rows
        let numCols = cols
        
        let (row, col) = position
        self.str = String(position.0)+"-"+String(position.1)
        
        // Check if the current position is within bounds and is part of the region
        guard row >= 0, row < numRows, col >= 0, col < numCols, matrix[row][col] == 1, !visited.contains(str) else {
            return
        }
        
        self.visited.insert(str)
        region.append(position)
        
        // Explore neighbors in all four directions
        dfs(matrix: matrix,rows: numRows,cols: numCols, position: (row - 1, col), visited: visited, region: &region)  // Up
        dfs(matrix: matrix, rows: numRows,cols: numCols,position: (row + 1, col), visited: visited, region: &region)  // Down
        dfs(matrix: matrix, rows: numRows,cols: numCols,position: (row, col - 1), visited: visited, region: &region)  // Left
        dfs(matrix: matrix, rows: numRows,cols: numCols,position: (row, col + 1), visited: visited, region: &region)  // Right
    }

好几处局部变量改成了属性，但还是不同位置报相同的错：Thread 1: EXC_BAD_ACCESS (code=2, address=0x16b6a7fc0)

完全不知道问题出在哪了，请大佬指点