503. Next Greater Element II

Given a circular array (the next element of the last element is the first element of the array), print the Next Greater Number for every element. The Next Greater Number of a number x is the first greater number to its traversing-order next in the array, which means you could search circularly to find its next greater number. If it doesn't exist, output -1 for this number.

Example 1:

Input: [1,2,1]
Output: [2,-1,2]
Explanation: The first 1's next greater number is 2; 
The number 2 can't find next greater number;
The second 1's next greater number needs to search circularly, which is also 2.

Note: The length of given array won't exceed 10000.

Rust Solution

struct Solution;

impl Solution {
    fn next_greater_elements(nums: Vec<i32>) -> Vec<i32> {
        let mut stack: Vec<usize> = vec![];
        let n = nums.len();
        let mut res = vec![-1; n];
        for i in 0..2 * n {
            let j = i % n;
            let x = nums[j];
            while let Some(top) = stack.pop() {
                if nums[top] < x {
                    res[top] = x;
                } else {
                    stack.push(top);
                    break;
                }
            }
            stack.push(j);
        }
        res
    }
}

#[test]
fn test() {
    let nums = vec![1, 2, 1];
    let res = vec![2, -1, 2];
    assert_eq!(Solution::next_greater_elements(nums), res);
}

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