Next greater element iii

Math Two Pointers String

35.2% acceptance

Jan 13, 2026

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495

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. Note that the returned integer should fit in 32-bit integer, if there is a valid answer but it does not fit in 32-bit integer, return -1.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn next_greater_element(n: i32) -> i32 {
    let mut digits: Vec<u8> = n.to_string().bytes().collect();
    let len = digits.len();
    // Find the rightmost digit that is smaller than the digit to its right
    let mut i = len as isize - 2;
    while i >= 0 && digits[i as usize] >= digits[i as usize + 1] {
      i -= 1;
    }
    if i < 0 { return -1; }
    let i = i as usize;
    // Find the rightmost digit greater than digits[i] to the right of i
    let mut j = len - 1;
    while digits[j] <= digits[i] {
      j -= 1;
    }
    digits.swap(i, j);
    digits[i + 1..].reverse();
    let result: i64 = digits.iter().fold(0i64, |acc, &d| acc * 10 + (d - b'0') as i64);
    if result > i32::MAX as i64 { -1 } else { result as i32 }
  }
}