# Minimum number of pairs required to make two strings same

Given two strings **s1** and **s2** of same length, the task is to count the minimum number of pairs of characters **(c1, c2)** such that by transforming **c1 to c2** or **c2 to c1** any number of times in any string make both the strings same.

**Examples:**

Input:s1 = “abb”, s2 = “dad”

Output:2

Transform ‘a’ -> ‘d’, ‘b’ -> ‘a’ and ‘b’ -> ‘a’ -> ‘d’ in s1.

We can not take (a, d), (b, a), (b, d) as pairs because

(b, d) can be achieved by following transformation ‘b’ -> ‘a’ -> ‘d’

Input:s1 = “drpepper”, s2 = “cocacola”

Output:7

**Approach:** This Problem can be solved by using Graphs or Disjoint Sets. Build an empty graph G and iterate through the strings. Add an edge in graph G only if one of the following conditions is met:

- Both
**s1[i]**and**s2[i]**are not in G. **s1[i]**is in G but**s2[i]**is not in G.**s2[i]**is in G but**s1[i]**is not in G.- There is no path from
**s1[i]**to**s2[i]**.

The minimum number of pairs will be the count of edges in the final graph G.

Below is the implementation of the above approach:

`# Python3 implementation of the approach ` `from` `collections ` `import` `defaultdict, deque ` ` ` `# Function which will check if there is ` `# a path between a and b by using BFS ` `def` `Check_Path(a, b, G): ` ` ` `visited ` `=` `defaultdict(` `bool` `) ` ` ` `queue ` `=` `deque() ` ` ` `queue.append(a) ` ` ` `visited[a]` `=` `True` ` ` `while` `queue: ` ` ` `n ` `=` `queue.popleft() ` ` ` `if` `n ` `=` `=` `b: ` ` ` `return` `True` ` ` `for` `i ` `in` `list` `(G[n]): ` ` ` `if` `visited[i]` `=` `=` `False` `: ` ` ` `queue.append(i) ` ` ` `visited[i]` `=` `True` ` ` `return` `False` ` ` `# Function to return the minimum number of pairs ` `def` `countPairs(s1, s2, G): ` ` ` `name ` `=` `defaultdict(` `bool` `) ` ` ` ` ` `# To store the count of pairs ` ` ` `count ` `=` `0` ` ` ` ` `# Iterating through the strings ` ` ` `for` `i ` `in` `range` `(x): ` ` ` `a ` `=` `s1[i] ` ` ` `b ` `=` `s2[i] ` ` ` ` ` `# Check if we can add an edge in the graph ` ` ` `if` `a ` `in` `G ` `and` `b ` `not` `in` `G ` `and` `a !` `=` `b: ` ` ` `G[a].append(b) ` ` ` `G[b].append(a) ` ` ` `count` `+` `=` `1` ` ` `elif` `b ` `in` `G ` `and` `a ` `not` `in` `G ` `and` `a !` `=` `b: ` ` ` `G[b].append(a) ` ` ` `G[a].append(b) ` ` ` `count` `+` `=` `1` ` ` `elif` `a ` `not` `in` `G ` `and` `b ` `not` `in` `G ` `and` `a !` `=` `b: ` ` ` `G[a].append(b) ` ` ` `G[b].append(a) ` ` ` `count` `+` `=` `1` ` ` `else` `: ` ` ` `if` `not` `Check_Path(a, b, G) ` `and` `a !` `=` `b: ` ` ` `G[a].append(b) ` ` ` `G[b].append(a) ` ` ` `count` `+` `=` `1` ` ` ` ` `# Return the count of pairs ` ` ` `return` `count ` ` ` `# Driver code ` `if` `__name__` `=` `=` `"__main__"` `: ` ` ` `s1 ` `=` `"abb"` ` ` `s2 ` `=` `"dad"` ` ` `x ` `=` `len` `(s1) ` ` ` `G ` `=` `defaultdict(` `list` `) ` ` ` `print` `(countPairs(s1, s2, G)) ` |

*chevron_right*

*filter_none*

**Output:**

2

## Recommended Posts:

- Minimum number of given operations required to make two strings equal
- Find the minimum number of preprocess moves required to make two strings equal
- Minimum Number of Manipulations required to make two Strings Anagram Without Deletion of Character
- Minimum edges required to add to make Euler Circuit
- Minimum deletions required to make GCD of the array equal to 1
- Minimum swaps required to make a binary string alternating
- Minimum array insertions required to make consecutive difference <= K
- Minimum operations required to make the string satisfy the given condition
- Minimum deletions required to make frequency of each letter unique
- Minimum operations required to make every element greater than or equal to K
- Minimum cost to make two strings same
- Minimum Cost To Make Two Strings Identical
- Minimum cost to make array size 1 by removing larger of pairs
- Minimum Cost to make two Numeric Strings Identical
- Minimum move to end operations to make all strings equal

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.