Given integers a & b, finds the largest permutation of digits in b that is smaller than a

DigitPermutations.py

################################################################
# Given integers a with digits a1 a2 ... am and b with digits
#b1 b2 ... bn find the largest permuation of b's digits so 
# b < a
################################################################

from itertools import permutations
import math

################################################################
def permSolver(a, b):
    #Initialize variables to store permutations and solution
    p = permutations(str(a))
    plist = []  #to store permutations in a more accessible way
    sol = -1
    
    #Loop to change permutations in p into more accessible list
    for i in p:
        str_perm = ""
        for j in i:
            str_perm = str_perm + str(j)
        str_perm = int(str_perm) 
        plist.append(str_perm)
    
    #Loop to find largest permutation smaller than 2nd number
    #Using max() to speed up process. Worst case still O(n)
    for i in plist:
        if max(plist) > b:
            plist.remove(max(plist))
        else:
            sol = max(plist)
            break
        
    return sol
################################################################
def findMax(a, b):
    a = str(a) #Turn into string for iteration
    ans = -1
    p = permutations(str(a)) #Collect all permutations
    
    for i in p:
        num = int("".join(i)) #Turn permutation into integers
        
        #Keeps largest number when smaller than b & no leading 0s
        if num <= b and i[0] != '0': 
            ans = max(ans, num)
    return ans
    

################################################################



num1 = 1234
num2 = 5678

#solution = permSolver(num1, num2)
#print(solution)
sol = findMax(num1, num2)

print(sol)





#n, m = input().split()
'''
n = "1234"
m = "5678"

m = int(m)
perms = permutations(n)

ans = -1
for p in perms:
    num = int(''.join(p))
    print(num, " ", p)

    if p[0] != '0' and num <= m:
        ans = max(ans, num)

print(ans)
'''