240. Search a 2D Matrix II

    func searchMatrix(_ matrix: [[Int]], _ target: Int) -> Bool {
        guard matrix.count > 0 && matrix[0].count > 0 else {return false}
        var n = matrix.count
        var m = matrix[0].count
        if target < matrix[0][0] || target > matrix[n - 1][m - 1]  { return false}
        var r = 0
        var c = m - 1
        while r < n && c >= 0 {
            if matrix[r][c] == target {return true}
            if matrix[r][c] > target { c -= 1}
            else if matrix[r][c] < target { r += 1}
        }
        return false
    }