Next Greater Element III — LeetCode 556 Python Solution

The problem

Given a positive integer n, find the smallest integer which has exactly the same digits existing in the integer n and is greater in value than n. If no such positive integer exists, return -1.

Example

Input

n = 12

Output

21

Python solution

class Solution:
    def nextGreaterElement(self, n: int) -> int:
        cs = list(str(n))
        n = len(cs)
        i, j = n - 2, n - 1
        while i >= 0 and cs[i] >= cs[i + 1]:
            i -= 1
        if i < 0:
            return -1
        while cs[i] >= cs[j]:
            j -= 1
        cs[i], cs[j] = cs[j], cs[i]
        cs[i + 1 :] = cs[i + 1 :][::-1]
        ans = int(''.join(cs))
        return -1 if ans > 2**31 - 1 else ans

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 556. Next Greater Element III is filed here because LeetCode tags it Two Pointers, which is the vocabulary this hub collects.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

Related problems