Next Greater Element III

Problem Given a positive 32-bit integer n, return the smallest integer that uses exactly the same digits and is strictly greater than n. If none exists within 32-bit range, return -1.

Input / Output

• Input: int n.
• Output: next greater permutation of n's digits, or -1.

Constraints

• n up to 2^31 − 1; answer must also fit in 32 bits.

Example

• n = 12 → 21; n = 21 → -1; n = 12443322 → 13222344.

Expected approach

• Next-permutation on the digit array: scan from the right for the first digit d[i] < d[i+1] (pivot); if none, return -1 (digits non-increasing → largest arrangement). Otherwise swap d[i] with the smallest digit to its right that is larger, then reverse the suffix after i to make it minimal. Check the 32-bit bound before returning. O(len) time, O(1) extra space.