Given a positive integer num consisting only of digits 6 and 9.
Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).
 
Example 1:
Input: num = 9669
Output: 9969
Explanation: 
Changing the first digit results in 6669.
Changing the second digit results in 9969.
Changing the third digit results in 9699.
Changing the fourth digit results in 9666. 
The maximum number is 9969.

Example 2:
Input: num = 9996
Output: 9999
Explanation: Changing the last digit 6 to 9 results in the maximum number.
Example 3:
Input: num = 9999
Output: 9999
Explanation: It is better not to apply any change.
 
Constraints:

1 <= num <= 10^4
num's digits are 6 or 9.

Difficulty: introductory

Starter code:

class Solution:
    def maximum69Number (self, num: int) -> int:
        

Solutions:
class Solution:
    def maximum69Number (self, num: int) -> int:
        numString = str(num)
        numLength = len(numString)
        firstIndex = numString.find('6')
        if firstIndex == -1:
            return num
        else:
            return num+3*10**(numLength-firstIndex-1)

class Solution:
    def maximum69Number (self, num: int) -> int:
        res = 0
        li = list(str(num))
        first = -1
        for i  in range(len(li)):
            if li[i] == '6':
                first = i
                break
        li[first] = '9'
        return int(''.join(li))

class Solution:
    def maximum69Number (self, num: int) -> int:
        ###############################################################
        # Solution 1, 
        # num_str = list(str(num))  # convert to string list 
        # if num_str == ['9']*len(num_str): # check if it needs change 
        #     return num 
        # else:
        #     for i in range(len(num_str)):
        #         if num_str[i] == '6': # chenge the '6' to '9'
        #             num_str[i] = '9'
        #             return int(''.join(num_str))
        
        ###############################################################
        # Solution 2, using just string 
        set_max = {9:9, 99:99, 999:999,9999:9999,6:9,66:96,666:966,6666:9666 }
        try:
            return set_max[num]
        except:
            num = str(num)
            for i in range(len(num)):
                if num[i] == '6':
                    return int(num[0:i] + '9' + num[i+1:])
        ###############################################################

        


class Solution:
    def maximum69Number (self, num: int) -> int:
        lst=list(map(int,str(num)))
        for i in range(len(lst)):
            if lst[i]==6:
                lst[i]=9
                break
        return int(''.join(map(str,lst)))

class Solution:
    def maximum69Number (self, num: int) -> int:
        
        n = list(str(num))
        for i in range(len(n)):
            if n[i] == '6':
                n[i] = '9'
                break
                
        return int(''.join(n))

import functools
class Solution:
    def maximum69Number (self, num: int) -> int:
        
        lmax = lambda xs: functools.reduce(lambda x, y: x+y, xs)
        print(lmax(['1','2','3'])) 
        str_num = list(str(num))
        for i in range(len(str_num)):
            if int(str_num[i]) == 6:
                str_num[i] = '9'
                break
        #str_num = ''.join(str_num)
        str_num = lmax(str_num)
        return int(str_num)

class Solution:
    def maximum69Number (self, num: int) -> int:
        str_num = list(str(num))
        for i in range(len(str_num)):
            if int(str_num[i]) == 6:
                str_num[i] = '9'
                break
        print(str_num)
        str_num = ''.join(str_num)
        return int(str_num)

class Solution:
    def maximum69Number (self, num: int) -> int:
        
        return int(str(num).replace('6', '9', 1))