221. Maximal Square

 func maximalSquare(_ matrix: [[Character]]) -> Int {
        guard matrix.count > 0 && matrix[0].count > 0 else { return 0}
        let n = matrix.count
        let m = matrix[0].count
        var dp = [[Int]](repeating: [Int](repeating: 0, count: m), count: n)

        var count = 0
        for i in  0 ..< n{
            for j in 0 ..< m {
                if matrix[i][j] == "1"{
                    dp[i][j] = 1
                    if i > 0 && j > 0 {
                        dp[i][j] = min(dp[i - 1][j] , dp[i - 1][j - 1], dp[i][j - 1]) + 1
                    }
                    count = max(count ,  dp[i][j] )
                }
            }
        }
        return count * count
    }