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Program to check whether string Is transformable with substring sort operations in Python
Suppose we have two numeric strings s and t, we want to transform from string s to t using the following operation any number of times: 1. Select a non-empty substring in s and sort it inplace so the characters are in ascending order. We have to check whether it is possible to transform string s into string t or not.
So, if the input is like s = "95643" t = "45963", then the output will be True because we can transform s into t using like "95643" -> "95463" -> "45963".
To solve this, we will follow these steps −
places := a map where default value type is list
for i in range size of s down to 0, do
key := s[i] as integer
insert i at the end of places[key]
for each e in t, do
key := e as integer
if places[key] is empty, then
return False
i := last element of places[key]
for j in range 0 to key - 1, do
if places[j] is non-empty and last element of places[j] < i, then
return False
delete last element from places[key]
return True
Example
Let us see the following implementation to get better understanding
from collections import defaultdict
def solve(s, t):
places = defaultdict(list)
for i in reversed(range(len(s))):
key = int(s[i])
places[key].append(i)
for e in t:
key = int(e)
if not places[key]:
return False
i = places[key][-1]
for j in range(key):
if places[j] and places[j][-1] < i:
return False
places[key].pop()
return True
s = "95643"
t = "45963"
print(solve(s, t))Input
"95643", "45963"
Output
True
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