Largest Number After Mutating Substring.py

class Solution:
def maximumNumber(self, num: str, change: List[int]) -> str:
    flag=0
    ls=list(num)
    for i in range(len(ls)):
        k=int(ls[i])
        if change[k]>k:
            ls[i]=str(change[k])
            flag=1
        elif flag==1 and change[k]<k:
            break
    
    return "".join(ls)