# Rearrange given string to maximize the occurrence of string t

• Last Updated : 23 May, 2019

Given two binary strings s and t. The task is to rearrange the string s in such a way that the occurrence of string t as a sub-string in s is maximum.

Examples:

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Input: s = “101101”, t = “110”
Output: 110110

Input: s = “10”, t = “11100”
Output: 10

Input: s = “11000100”, t = “101”
Output: 10101000

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: If we can not make any occurrence of string t in string s then output any permutation of s. Otherwise, start the rearranged string with t. Now we will make the next occurrence of string t in string s as left as possible in order maximize the count of occurrence. To achieve this we will find the largest suffix of string t that matches the prefix of string t
of the same length. It can be found by Prefix Function, Z-Function or Hashes.

Below is the implementation of the above approach:

 `# Python3 implementation of the approach ``from` `collections ``import` `defaultdict`` ` `# Function to return the length of maximum ``# proper suffix which is also proper prefix``def` `Prefix_Array(t):``    ``m ``=` `len``(t)``    ``arr ``=``[``-``1``]``*``m``    ``k ``=``-``1``    ``for` `i ``in` `range``(``1``, m):``        ``while` `k>``-``1` `and` `t[k ``+` `1``]!``=` `t[i]:``            ``k ``=` `arr[k]``        ``if` `t[k ``+` `1``]``=``=` `t[i]:``            ``k``+``=` `1``        ``arr[i]``=` `k``    ``return` `arr[``-``1``]`` ` `# Function to return the rearranged string``def` `Rearranged(ds, dt):``    ``check ``=` `Prefix_Array(t)`` ` `    ``# If there is no proper suffix which is ``    ``# also a proper prefix``    ``if` `check ``=``=``-``1``:``        ``if` `ds[``'1'``]``0``:``                ``temp``+``=``'1'``                ``ds[``'1'``]``-``=` `1``            ``while` `ds[``'0'``]>``0``:``                ``temp``+``=``'0'``                ``ds[``'0'``]``-``=` `1`` ` `            ``# Return the rearranged string``            ``return` `temp`` ` `        ``# If count of 0's in string t is 0 ``        ``if` `dt[``'0'``]``=``=` `0` `and` `ds[``'1'``]!``=` `0``:``            ``n ``=` `ds[``'1'``]``/``/``dt[``'1'``]``            ``temp ``=` `t ``*` `n``            ``ds[``'1'``]``-``=` `n ``*` `dt[``'1'``]``            ``while` `ds[``'1'``]>``0``:``                ``temp``+``=``'1'``                ``ds[``'1'``]``-``=` `1``            ``while` `ds[``'0'``]>``0``:``                ``temp``+``=``'0'``                ``ds[``'0'``]``-``=` `1``                 ` `            ``# Return the rearranged string``            ``return` `temp``             ` `        ``# If both 1's and 0's are present in``        ``# string t``        ``m1 ``=` `ds[``'1'``]``/``/``dt[``'1'``]``        ``m2 ``=` `ds[``'0'``]``/``/``dt[``'0'``]``        ``n ``=` `min``(m1, m2)``        ``temp ``=` `t ``*` `n``        ``ds[``'1'``]``-``=` `n ``*` `dt[``'1'``]``        ``ds[``'0'``]``-``=` `n ``*` `dt[``'0'``]``        ``while` `ds[``'1'``]>``0``:``            ``temp``+``=``'1'``            ``ds[``'1'``]``-``=` `1``        ``while` `ds[``'0'``]>``0``:``                ``temp``+``=``'0'``                ``ds[``'0'``]``-``=` `1``        ``return` `temp`` ` `    ``# If there is a suffix which is ``    ``# also a prefix in string t``    ``else``:``        ``if` `ds[``'1'``]``0``:``                ``temp``+``=``'1'``                ``ds[``'1'``]``-``=` `1``            ``while` `ds[``'0'``]>``0``:``                ``temp``+``=``'0'``                ``ds[``'0'``]``-``=` `1``            ``return` `temp`` ` `        ``# If count of 1's in string r is 0``        ``if` `dr[``'1'``]``=``=` `0` `and` `ds[``'0'``]!``=` `0``:``            ``n ``=` `ds[``'0'``]``/``/``dr[``'0'``]``            ``temp``+``=` `r ``*` `n``            ``ds[``'0'``]``-``=` `n ``*` `dr[``'0'``]``            ``while` `ds[``'1'``]>``0``:``                ``temp``+``=``'1'``                ``ds[``'1'``]``-``=` `1``            ``while` `ds[``'0'``]>``0``:``                ``temp``+``=``'0'``                ``ds[``'0'``]``-``=` `1``            ``return` `temp`` ` `        ``# If count of 0's in string r is 0``        ``if` `dr[``'0'``]``=``=` `0` `and` `ds[``'1'``]!``=` `0``:``            ``n ``=` `ds[``'1'``]``/``/``dr[``'1'``]``            ``temp``+``=` `r ``*` `n``            ``ds[``'1'``]``-``=` `n ``*` `dr[``'1'``]``            ``while` `ds[``'1'``]>``0``:``                ``temp``+``=``'1'``                ``ds[``'1'``]``-``=` `1``            ``while` `ds[``'0'``]>``0``:``                ``temp``+``=``'0'``                ``ds[``'0'``]``-``=` `1``            ``return` `temp`` ` `        ``# If string r have both 0's and 1's``        ``m1 ``=` `ds[``'1'``]``/``/``dr[``'1'``]``        ``m2 ``=` `ds[``'0'``]``/``/``dr[``'0'``]``        ``n ``=` `min``(m1, m2)``        ``temp``+``=` `r ``*` `n``        ``ds[``'1'``]``-``=` `n ``*` `dr[``'1'``]``        ``ds[``'0'``]``-``=` `n ``*` `dr[``'0'``]``        ``while` `ds[``'1'``]>``0``:``            ``temp``+``=``'1'``            ``ds[``'1'``]``-``=` `1``        ``while` `ds[``'0'``]>``0``:``                ``temp``+``=``'0'``                ``ds[``'0'``]``-``=` `1``        ``return` `temp`` ` `# Driver code``if` `__name__``=``=``"__main__"``:``    ``s ``=``"10101000"``    ``t ``=``"101"`` ` `    ``# Count of 0's and 1's in string s``    ``ds ``=` `defaultdict(``int``)`` ` `    ``# Count of 0's and 1's in string t``    ``dt ``=` `defaultdict(``int``)``    ``for` `i ``in` `s:``        ``ds[i]``=` `ds[i]``+``1``    ``for` `i ``in` `t:``        ``dt[i]``=` `dt[i]``+``1``    ``print``(Rearranged(ds, dt))`
Output:
```10101000
```

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