Find Permutation — LeetCode 484 Python Solution

The problem

A permutation perm of n integers of all the integers in the range [1, n] can be represented as a string s of length n - 1 where: s[i] == 'I' if perm[i] < perm[i + 1], and s[i] == 'D' if perm[i] > perm[i + 1]. Given a string s, reconstruct the lexicographically smallest permutation perm and return it.

Example

Input

s = "I"

Output

[1,2]

Explanation

[1,2] is the only legal permutation that can represented by s, where the number 1 and 2 construct an increasing relationship.

Python solution

class Solution:
    def findPermutation(self, s: str) -> List[int]:
        n = len(s)
        ans = list(range(1, n + 2))
        i = 0
        while i < n:
            j = i
            while j < n and s[j] == 'D':
                j += 1
            ans[i : j + 1] = ans[i : j + 1][::-1]
            i = max(i + 1, j)
        return ans

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 484. Find Permutation is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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