Program to find circular greater element to the right in Python

Python Server Side Programming Programming

Suppose we have a list of numbers called nums. We have to find a new list of the same length where the value at index i is assigned to the next element greater than nums[i] to its right, circling back to the front of the list when required. If there is no number that is greater, then it should be set to -1.

So, if the input is like [4, 5, 1, 3], then the output will be [5, -1, 3, 4]

To solve this, we will follow these steps−

n := size of a
stack := a stack, insert 0 initially, res := a list of size n and fill with -1
for each value in range 0 and 1, do
- for i in range 0 to n-1, do
- while stack is not empty and a[top of stack] < a[i], do
  - res[top of stack] := a[i]
  - delete last element from stack
- insert i at the end of stack
return res

Let us see the following implementation to get better understanding −

Example

Live Demo

class Solution:
   def solve(self, a):
      n = len(a)
      stack, res = [0], [-1] * n
      for _ in range(2):
         for i in range(n):
            while stack and a[stack[-1]] < a[i]:
               res[stack[-1]] = a[i]
               stack.pop()
            stack.append(i)
   return res
ob = Solution()
nums = [4, 5, 1, 3]
print(ob.solve(nums))

Input

[4, 5, 1, 3]

Output

[5, -1, 3, 4]

Arnab Chakraborty

Updated on 05-Oct-2020 13:09:30

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