Program to find length of longest increasing subsequence in Python

PythonServer Side ProgrammingProgramming

Suppose we have a list of numbers. We have to find the length of longest increasing subsequence. So if the input is like [6, 1, 7, 2, 8, 3, 4, 5], then the output will be 5, as the longest increasing subsequence is [2,3,4,5,6].

To solve this, we will follow these steps −

  • Make an array called tails whose size is same as nums, and fill this with 0.

  • size := 0

  • for each element x in nums array −

    • i := 0, j := size

    • while i is not same as j, then

      • mid := i + (j – i)/2

      • if tails[mid] < x, then i := mid + 1 otherwise j := mid

    • tails[i] := x

    • size := max ofi + 1 and size

  • return size.

Let us see the following implementation to get better understanding −

Example

class Solution(object):
   def solve(self, nums):
      tails =[0 for i in range(len(nums))]
      size = 0
      for x in nums:
         i=0
         j=size
         while i!=j:
            mid = i + (j-i)//2
            if tails[mid]> x:
               i= mid+1
            else:
               j = mid
         tails[i] = x
         size = max(i+1,size)
      return size

ob = Solution()
nums = [7, 2, 8, 3, 9, 4, 5, 6]
print(ob.solve(nums))

Input

[7, 2, 8, 3, 9, 4, 5, 6]

Output

5
raja
Published on 10-Oct-2020 16:39:14
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