Program to find number of swaps required to sort the sequence in python

Suppose we have a list of distinct numbers; we have to find the minimum number of swaps required to sort the list in increasing order.

So, if the input is like nums = [3, 1, 7, 5], then the output will be 2, as we can swap 3 and 1, then 5 and 7.

To solve this, we will follow these steps:

• sort_seq := sort the list nums
• table := a new map
• for each index i and value n in nums, do
  • table[n] := i
• swaps := 0
• for i in range 0 to size of nums, do
  • n := nums[i]
  • s_n := sort_seq[i]
  • s_i := table[s_n]
  • if s_n is not same as n, then
    • swaps := swaps + 1
    • nums[s_i] := n
    • nums[i] := s_n
    • table[n] := s_i
    • table[s_n] := i
• return swaps

Let us see the following implementation to get better understanding:

Example Code

Live Demo

class Solution:
def solve(self, nums):
   sort_seq = sorted(nums)
   table = {}

   for i, n in enumerate(nums):
      table[n] = i
   swaps = 0
   for i in range(len(nums)):
      n = nums[i]
      s_n = sort_seq[i]
      s_i = table[s_n]

      if s_n != n:
         swaps += 1
         nums[s_i] = n
         nums[i] = s_n
         table[n] = s_i
         table[s_n] = i

      return swaps

ob = Solution()
nums = [3, 1, 7, 5]
print(ob.solve(nums))

Input

[3, 1, 7, 5]

Output

2

Arnab Chakraborty

Updated on: 25-Nov-2020

1K+ Views

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